API Course for Beginners 2026 | API Tutorial For Beginners Step By Step | API Tutorial | Simplilearn

Key Takeaways

[Music] You have used APIs more times than you realize, but have you ever wondered what happens behind the scenes when your app fetches weather data or even when your browser shows your search results from Google? How does it get that information in real time? And that's the power of APIs which is application programming interface systems that let different applications talk to each other and share data instantly. In this course, we will be learning how API works step by step. You'll understand exactly how APIs make internet so dynamic and more importantly how to use them in your own applications. We'll start with fundamentals of what API is, then move on to setting up the tools you need, making your first API request, working with different types of data, and even creating your own APIs. By the end of this course, you won't just know the theory, you'll have a hands-on using APIs in real world applications. This course is practical, engaging, and designed for beginners with basic programming knowledge to follow along and start working with API confidently. If you are interested in knowing about how generative AI works and want to take this knowledge to a professional level, there is a opportunity waiting for you. The applied generative AI specialization by Purdue University and simply learn is a live hands-on program where you actually build real gen AI and agentic AI applications using tools like lang chain, Azure AI studio and hugging face. It's a 16-week live online certification taught by industry experts and Perurdue faculty and you even get Purdue alumni association access for global networking. By the end, you'll have seven plus projects under your belt from AI power HR assistance to rag based BI dashboards. So, if you're ready to turn your learning into real career edge, check out the link in the description box below and in the pin comments and explore the program. Before we dive deeper into the concepts, let's start with a quick quiz. What do you think API is? Is it a chat application, a system that allows apps to communicate, a tool for creating websites, or a program that makes calls? Let us know your answers in the comments below. Before we start with the practical part, let's first answer the important question. What exactly is an API? An API is a set of rules that allows different software application to talk to each other. It's like a bridge connecting two different applications letting them communicate without needing to understand how the other works. Think of API like a waiter at a restaurant. You who is a customer tell the waiter what you want. The waiter that is the API communicates your request to the kitchen which is the system and brings back the food which is the data. The API doesn't process the data or decide what to do with it. It just transforms the requests and delivers the response from one system to another. In simpler terms, API allows different software systems to exchange data and services making them essential part of modern applications. Now that we know what APIs are, let's discuss why they are so important. APIs exist because they solve a critical problem which is communicating between different application. Instead of building everything from scratch, developers can use external APIs to add powerful features to their applications without even reinventing the wheel. For example, weather apps don't create their own weather data. They rely on open weather API to fetch realtime weather data from external sources. Payment gateways like Stripe or even PayPal provide APIs that let you securely process payments in your app without handling the sensitive financial data directly. Social media apps uses APIs to allow apps to share posts, retrieve messages, or even log onto other apps. By using APIs, developers can integrate data and services from various platforms and create featurerich applications without having to build everything themsel. Now that we understand what an API is and why they exist, let's take a look at how APIs actually work in simple real world scenario. The process using an API typically involves three steps. Step one is to send an API request. You who is the client sends an API request to a specific API endpoint. For example, you might send a get request to an API to retrieve some data like fetching the current weather. Step two is the API processes the request. The API then takes the request, processes it, and typically communicates with the backend server or database to retrieve the requested data or perform an action. Step three is to receive the response. The API returns a response to the client. The response is typically in JSON format which is JavaScript object notation a lightweight data format that easy for both humans and machines to read. For example, if you request weather data, the server might respond with information like temperature is 22° C, condition of clear sky. Now there are a couple of ways to send the API request and some of them are as follows. There are other tools and methods to interact with APIs. These tools provide different features and interfaces. Some of which are user-friendly and other more suited for advanced users or specific environments. Here's an overview of various way to execute the APIs. The first way is to use Postman. It has both web and desktop tool. So to open it, we just need to type www.postman. And here you can see. Now since it is both web and desktop, for desktop you just need to download it. So here you can see you can download it for Windows, Mac and other Linux systems and you can use website too. I'll be using website because it's more convenient way without any installation process. Now why did I choose Postman is it is because it is a powerful and popular tool used by developers for testing the APIs. It allows you to send requests, view responses, organize API requests into collections. It is often used for manual testing and debugging too. Now what are the some of the permissions required? The first permission will be about your API key or even OOTH tokens for authentication. Now later I'll tell you what are API keys and OOTH tokens for authentication. So these two are a must for an API. And then we need to support both get and post method as well as others like put and delete. For example, if you interact with public APIs like JSON, placeholder or authenticate using services like open weather app by providing your API key. Other tools instead of postman you can use is as I told you you can use website. Now Postman web allows you to use the tools directly from the browser without any installation. So this is the interface of Postman. I'll explain you all the details of the workspace, how to use it etc. So simple things such as uh your email address, password, a strong password, authentication will be required to set up a free account. The second alternative will be insomnia. So if you give insomnia rest, that will be the page appearing here. There's a free trial for you guys. It is similar to Postman. So you'll be able to work with a similar interface. Again, it's another popular API testing tool that offers a clean user interface and supports all the commands such as REST, GraphQL, and websocket API. It is also great for both advanced and beginner friendly users. Now, again, what are the permissions required here? As usual, we need API keys and ooth tokens for authenticated APIs. It can handle custom headers and body data just like a postman. Now where and all are you going to use insomnia? It is for testing APIs with custom headers or even while working with GraphQL queries. So the third option will be curl. To open that you can just type in curl.se and this page will appear. So as you can see here in lib curl we have API as an option and you have all the information. It's a easy interface. Free versions are also available for users who prefer the command line. curl is a versatile tool used for making API requests. It supports a wide variety of protocols like HTTP, HTTPS and FTP. It's idle for a quick test or when automatic API calls in scripts. Now again the permissions include the API keys and the header of authenticated requests. Here there is one more point where custom headers and data are included directly in the command. Another alternative API tool will be swagger. So to open that it's swagger.io. Now as swagger is a part of open AI. It is a tool set that helps developers document and interact with APIs. It provides a graphical interface where you can execute APIs request directly from the documentation page. So you don't need to copy and paste it. It by default takes all. It also depends on the API being used. So you might need an API key or OOTH credentials. Swagger UI typically works with APIs that follow the open API specifications allowing automatic documentation generation. Now again if you have an API that's documented in OpenAI, you can test the endpoints directly using Swagger UI which is often hosted online or integrated into the web page. The fifth alternative will be rapid API. Again we have rapid API.com. So this is the initial page. Rapid API is a marketplace for the APIs. It provides a web platform where you can find the APIs, view their documentation and execute requests directly through the website. The required permissions will be API keys and typically required for many of the APIs listed on the platform. Now when and where you can use rapid. You can use rapid API to explore APIs like Twitter API, weather API and many others all from one platform making it easy to test multiple APIs with just one account. Now another option is a browser one. Simple get request can be executed via browser. This method is very limited to fetching data from APIs that don't require complex requests, bodies or authentication like a public API. For a basic get request to public APIs, no permission are usually required. A requiring authentication can't be tested this way. You can use a browser to visit the URL. Like suppose you're using JSON placeholder, you can just type in httpsjson placeholder.typode.com typcode.com post to retrieve data. Now apart from all these online API testing tools which are the equal replacement of postman are Requin. Again Rebin is a very similar tool to Postman. It is a free version where you can execute few of the comments here. As you can see it is a web-based tool where you can test APIs in online without installation of any software. You can send, get, post, put, patch, delete, head and options here and also you can send the request and view the response directly in the browser itself. Now apart from this there is another web browser. Apart from this another website tool is API Penny which is a Chrome extension for Google Sheets that allows you to send API requests and load the response data into the spreadsheets directly. So for that you can just head into apipen.io. Now that we understood the concept of APIs, let's move on to testing APIs using Postman web. Now that we have understood the concept of APIs, let's move on to testing APIs using the Postman web, a popular tool used by developers to interact with APIs. Postman is a powerful tool that allows us to send the requests to APIs and view the responses. In this part, we'll walk through the Postman's interface, learn how to make requests and understand how to read the response from the API. Again to start with Postman web, you can just type in Postman and open the web interface. It has simple normal details which is your mail ID and set a strong password. And since it is a free tool, you don't need to pay anything. You can execute all kinds of commands in the free version itself. Although it has number of request per day or per minute set to thousand. When we talk about interacting with APIs, Postman is a tool that makes it easy to test API calls. It allows you to send requests to an API and view the response in a structured way. Let's look at Postman web interface to see where everything is located, how to use it effectively. Now, this is the interface of the Postman. So first thing that gets us is the different kinds of requests that you can send the API. The first one is get. Then we have post, port, patch, delete, head and options. So you can select which kind of a command, enter the URL and just hit on the send button. And here will be your collection of your previously executed commands. Here you can add a workspace blank collections. You can name it. You can organize all your commands here which you have already given. There's also environment, history, flows and more options. Now coming to here we have different kinds of documents that is attached to a particular request. We have parameters. So when you paste a URL suppose a placeholder the parameters will be added here. We have authorizations, headers, body, scripts and few of the settings are given here. So for each request you can set it accordingly. Now the first request will be get which is basically retrieving the data for example like weather or post and the second one is post. This is to send the data to create or update resources. So any kind of data you want to update which is already present you can use the post command. Next we have the put is like updating existing data and then delete obviously as you know remove data. So we'll take a look out others in the future coming modules. Now coming to the URL part which is a central part of the interface. This is where you enter the endpoint you want to interact with and also it is specifically the URL of the API you are testing. For example, to get users data from JSON placeholder, you will enter the JSON placeholder.code.com post. For example, to get the user data from a JSON placeholder, you'll just need to enter the API course until where you have got the website from the API course.code.com and since you want the information of the users, you'll print / users. The next important thing is parameters. This sections allows you to pass query parameters to the API. For instance, when you're querying a weather API, you might pass the city name as a query parameter. Next to that, we have authentication. If the API requires an API key which is given in other websites or open in some few need authentication to get your API key, you would add it in here. This is where you manage any kind of authentication. Next we have body. When making a post request which is sends data. This is where your input of the body of the requests will be present. For example, you might want to send a new user's data in JSON format. So you just need to type in which format of data will be sent and type the code. Now coming here to the response section. After sending any kind of request, the response section at the bottom shows the data returning by the API. This is where you will see the status code, headers and body usually in a JSON format. Now the main part is how do we get this URL. Now let's break down the URL and see how you can make requests. The URL format usually looks something like this. The first one will be the base URL. the main part of the URL where the API is hosted. For example, in httpsjson placeholder.tapcode.com. This entire thing is the base of the command. Next, we have the endpoint. Here we have given users as the endpoint since we want the user data. This specify the resources you want to access. Combine these both together, it will give you a full API endpoint. Now when you execute this here you can see there is users name, city, zip code, geographical location which is returned. Now coming to some of the APIs that allow you to pass parameters in the URL such as search filters. These come after the symbol of question mark. For example, again we'll take consider JSON placeholder users and just we'll give a conditional statement which is question mark name is equal to is equal to let's keep Len Graham which is the first we got. So here we are giving it a condition to print all the users details where name is Len Graham. So when you send the request there is none like that. So there's a spelling error. So let's just change that. And now if you send it, it'll be printing whatever name matches this len part. Now let's get into detail about each of the commands. First one is get which is fetching the data. A get request is used to retrieve data from the server. It is most common and simplest HTTP method and it does not alter any data on the server. A get request only fetches data making it safe and independ. It is commonly used when you need to read data from an API such as fetching user profiles, posts or other resources. Now again when it is used when you want to fetch any kind of data without making any changes to the resources or the server for example fetching post, user or even weather data. Now let's execute one of the get command and see how it works. So again as usual the first is you have to select the get and in the URL field enter the endpoint for which you want to interact with. For example to fetch users as we executed earlier we have users and you can just click on send. Now here postman will display the response in a lower section of the window which is a response window. You will receive a JSON response with requested data. So you here you can see each ID is given, name is given, username, email address. This is a individual users name and their details. Now coming to post request, the second part which is sending the data. A post request is used to send data to the server typically to create a new resource. When using post, you send data in request body which then is processed and stored on server. Unlike get, post changes the state of the server by adding or even modifying the resources. When it is used, you need to create a new resource or submit data to the server, then you can use the post command. For example, submitting a form, creating a new post, or even sending data to be processed uses the post command. Now let's execute one of the post command. The first step is to select post here. Now let's enter the URL. So instead of users, I'm going to put posts and run it. So as you see here, we found 4.4 not found. But before that we need to go to the body and from there you need to select so that you can enter what kind of a data you want to send it. So let's put this response tab back. So here you select raw. So here you select raw and then there is a drop-own. You can use text, JavaScript, JSON, HTML or XML. So let's go with JSON since it is a very common way. Now here you can add what kind of information you want to send it. So here I'll be adding title in the same format as we receive the data and then let's say new post and follow that by a body in a body. Let's say this is a new post and then you can add information such as user ID etc. For now, I'm just giving the title and the body and you can click on send and the data will be modified. Moving on to the next request, we have put. Put request is used to update an existing resource with a new data. It replaces the entire resource with a new data provided in the request body. So let's say put requests are typically used when you want to overwrite the resources entirely. Now again when to use it when you need to update an existing resource completely for example updating a user's profile or modifying a product's information. Again the same steps to follow. We have to choose put and enter the URL and whatever changes you want to do you can do it in a JSON format. Again here I've added in the JSON format choosing the raw in the body and then you can just click on send. We'll take a look at the errors and what it meant in the later. Now if it is actually a good command if it runs it will show you the response with the updated resource. Next we have patch. Now what it does is a patch request is used to make partial updates to an existing resource unlike port patch only updates the specified fields and leaves the other data unchanged. It's often used for smaller incremental updates to a resource. Now when it is used when you need to update only specific fields of an resource without replacing the entire resource. For example, for updating only the title or description of a post. The patch also follows a similar kind of approach. So you can select patch here. Enter the URL. Go to raw in a JSON format or any other format which you're comfortable in. We can give the new data and here you can only add the fields you want to update. Then you can just click on send and then you can take a look at the response which will print the entire change resources. Next we have delete. A delete request is used to remove a resource from the server. Once a resource is deleted, it is no longer accessible or even retrievable. When you want to delete a resource from the server, for example, deleting a post, removing a user, or even removing an item from your cart. Again, to execute it, you just need to set it to delete. Enter the URL and then you can just click on send. Let me just clear the body up and none. And you can just click on send and it is executed. A successful delete request will return a 200 with no updated data here since it is already deleted. The next we have head. A head request is similar to a get request but it only retrieves the header of the response not the body. It is useful for checking metadata such as content type or length without downloading the full content. When are they used? when you need to check metadata or headers for resources without downloading the body. For example, checking if a resource exist or inspecting responses headers like content type, content length, etc. Again, similar way of executing head. Select the head in the drop-own menu. Add the URL. This URL will be mentioned as API URL. And then you can just click on send. Since this URL we have deleted it, it's not showing anything. But if it's a proper command, Postman will display only the headers in the response with no body. Lastly, we have options. What it does is an option request is used to determine which HTTP methods are allowed for a specific resource. It is often used to discover which action can be performed on the resource and is helpful in course. Now, what is course? It's cross origin resource sharing. When are they used? When you want to find out which HTTP methods are allowed for a resource. For example, determining if an endpoint supports post, get, port, etc. Similar way of execution of options. Select the drop-own menu. Click on options. Enter the API URL and just click on send. Now, since it is an empty URL that we have mentioned, it is showing no content. Usually Postman will show the allowed methods for the resource in the allowed header for the response. So when I executed so many URLs, there was this number that it was popping. Many kind of numbers were popping. So let's take a look at what kind of numbers and what it suggests. When an API responds to a request, it typically includes a status code, a message which is commonly called as a status code. So if it is 200 okay it means the request was successful. If it is 400 bad request the request is malformed. If it is 4.1 unauthorized the API key is missing or it might be invalid also. And then we have 4.4 not found the request resources doesn't exist. Here's how you interpret the JSON's response. The body of the response contains the data that was requested. The status code tells you whether the request was successful. Now you have learned how to test APIs using Postman web. You know how to send get requests to fetch data, post request, submit the data, or even view the response from the server. Next, we'll explore how to handle headers, authentication, and error handling when interacting with APIs. Now that we have learned how to interact with APIs and understand basic request or even response cycles, let's take a step further by looking at the advanced feature of API interaction. We'll learn how to authenticate requests and use headers and handle errors that may come up while working with the APIs. API authentication is crucial when interacting with third-party services as it ensures that only authorized users can access the data or services. Additionally, understanding how to handle errors in API response will make your application more robust and userfriendly. The first step is API authentication. Many of the APIs require authentication to ensure that only authorized users or system can access certain data or perform certain actions. Authentication usually happens via API keys or OOTH tokens or other methods. The first one is API key authentication. One of the simplest ways to authenticate is by passing an API key in the request header or even in the query parameter. The second type is OOTH authentication where OOTH tokens are most secure and used for more sensitive operations. They require an authentication process to get the token. Now let's take a look at how to add an API key to the request in Postman. Now here as an example, I'm going to take weather API from open weather map. So you just type in open weather map again for different data that you want there'll be different API or website that are provided with different API. So just log to your account with a good password. Now here you can see an option of API. Just click on it. So from this page you can open your profile here and you can see here my services, my API keys, payments profile and log out. So you can just click on my API keys and here you can see it may ask you to register again with your email and password and here are the keys. You will already have one default key and you can create it according to your project. So we can create it. Give it a name and generate it. So here you can see we have weather as generated. These are my previous active keys. Make sure you don't share these with any of the people so they can get access to the data with your profile. So if you're not using just deactivate them and cancel it out. So this is your API key. So let's just copy it. Come back to the postman and there is authentication tab here. Okay. So as usual how to start the URL. So we have http dot the website that you have used to get the API key. So we have API and which website did we get in? We have open weather map.org and then what are we accessing the data? What is the version 2.5 and we need weather data and then here we have conditional statement which is Q is equal to you can mention whichever state or city's weather ID you need. So let's take an example of London and also let's give another condition aid will be equal to your API code. So whatever API code that you have copied from the weather app or website which is this one you can just copy it and paste it over here and just send it. So if you execute that particular URL here you can see we have code London latitude and longitude the weather main is clouds over the clouds and icon is 04D. Now coming to advanced authentication which is the OOTH 2.0. OOTH 2.0 is more secure authentication method often used by APIs that require access to sensitive data such as user accounts or even payment system. 2.0 involves multiple step where you must first authorize the user and then obtain an access token to make requests. Now how do you perform this oorthth? So this is the parameters when you come to authentication here you can see ooth type and here we have bearer token JWT bearer digest o 1.0 and 2.0 since the latest one is 2.0 Z just click on that and let me just show you what are the things you have to fill out to get the tokens. Here we have request either by URL or headers and then we have the tokens available tokens. As of now we have no tokens available and then we have a header prefix which is usually barrier itself and then we have to give a name to the token the authentication code via which implicit or password credential or even client credentials. We have a call back URL and O URL access token URL which should be filled and we have to mention the client ID client secret scope state and even client authentication. Now when you all set these you will see here the key values token request what are the key values send in and then you can click on get new access token and you'll be getting the tokens. Now be aware these credentials are very important and it will be given by the client side who you're working for. Now that you know how to authenticate requests, work with headers and handle errors, it's time to take things to a next level. We'll be exploring three advanced features. The first one is pagionation. Now what is pagenation? When an API return large sets of data, we need a way to break it down into smaller chunks. The quers for these are allows us to filter, sort or modify databases on specific criteria. Then we have rate limiting. We'll also learn about how some APIs limit the number of requests we make in a certain time frame and how to manage them effectively. APIs often deal with large data sets and sending all of that at once might overwhelm both the server and the client. Pagionation helps by splitting the data into smaller chunks. This is also known as pages. While using pagenation, you'll often pass parameters like page and limit in the query. Now, how does pagionation works? The first parameter is page. This specifies which page of data you want to fetch and the second one is limit. This defines how many items you want to fetch per page. For example, let's say we want to fetch user data from JSON placeholder but we only want to see five users at a time. So what will be the URL here? So firstly we'll go to the JSON one. So we'll get the base right. And here since we are filtering the users let's say users and now here as per the part of the condition we have page is equal to 1 and also I'll add a combined condition which is and let's say limit up to five. Now here I have mentioned / page is equal to 1. This fetches the first page of the data and I've also given limit as five. So again this limits the results to five users. So let's get it and check. As you can see query parameters have also changed here. We have added page and limit here. And when you execute it, so the execution was okay. That means it has run successfully. And you can observe the first page file limit repeat. If you want to change that to three, let's just limit it to three users and you'll get only three users details. Now the second one is query parameters which is filtering and customization of data. Query parameters are key value pairs included in the URL that let us filter, modify or pageionate data from the API. They are very useful when you want to get specific data such as searching for users with a certain name or filtering results by certain category. For example, if you want to filter users by name from the JSON placeholder API, you would use a query parameters like this. So as told before we have users and let's just type in name is equal to let's just copy and paste this since we need a result and execute this. Now here if the name matches the name that you have given it will give you a reply back with that particular ID and the username which is matching and the related data. The third advanced feature here will be rate limiting. Most APIs have a rate limit, meaning they restrict how many requests you can make in a certain time frame, for example, thousand requests per hour. This is done to prevent excessive load on the server and ensure fair use for everyone. When you hit the rate limit, you'll often receive a 429 status code, which is too many requests. It usually provide the remaining number of requests in a response header. Now how to handle this rate limiting in Postman? Some APIs include information about rate limit in the response header. So you can just open the response header here and you can go down. You'll find X rate limit which is 1,000 and X rate limit remaining is 999. So only one request we have sent and we can execute about 999 request in an if you reach the limit wait until the time window resets before making more. Now let's combine query parameters and rate limiting. This will make more efficient request. For example, you might want to filter users by name and only fetch five results at a time. Now here what will be the URL? So we are giving JSON placeholder dot type code users name we are filtering the name by line and we are giving a page of five and limit of five. So if there is any user which is so this comment states that if any name which is matched by Lenny and in the page one within the limit of first five the answer will be printed if these conditions are met. request filters by the name Lenny returns five users per page and get the first page. To handle rate limiting, you can monitor your remaining requests and make sure you're not exceeding the limit by checking the response headers. So these were the basics of API and how to use them, how to get them, how to make use of them. So here's a challenge for you people. So here's a exercise for you people. create a weather app or any kind of app which uses the API authentication in any kind of online web browser. You can choose Postman or any other thing which is comfortable for you to use. Other things which I've given options at the starting you can use them and let me know in the comment section below which online web browser are easy for you guys to use it. You have completed the API basics for beginners course. You have learned how to interact with APIs using tools like Postman and Python. How to send get and post requests, work with JSON data, handle authentication, manage errors, and much more. By now, you should feel confident in your ability to send requests and understand the responses. Whether you're working with public APIs or creating your own, the skills you have gained will be invaluable as you continue to build dynamic datadriven applications. But don't stop here. Keep experimenting with APIs. Explore more complex interactions and start integrating APIs into your own projects. The possibilities are endless. Remember, API are the backbone of modern web development. And as you continue to explore new tools and frameworks, you will see how powerful they can be. So, keep coding, keep learning, and keep building. If you found this course helpful, don't forget to like, subscribe, and leave a comment below with any questions or ideas for future topics. Until next time, keep learning with Simply Learn.