An Introduction to APIs: What They Are and How They Work

Imagine trying to build a house without pre-made materials – you’d have to craft every brick, pipe, and wire from scratch. That’s what software development would be like without APIs. APIs are the digital building blocks that enable applications to communicate, share data, and extend functionality without developers having to reinvent the wheel.

Whether you’re checking the weather on your phone, logging into a new app with your Google account, or tracking your website’s performance in a marketing dashboard, you’re using an API, often without even realizing it.

But what exactly is an API, and how does it work?

In this beginner-friendly guide, I’ll break down the basics of APIs in plain English – what they are, how they function, and why they’re so essential in today’s connected world. Even if you’re not a developer, understanding APIs can help you automate workflows, improve website performance, and even unlock smarter SEO strategies.

What is an API?

API stands for Application Programming Interface. 

It’s essentially a way for two different software systems to communicate with each other in a structured, reliable way. It defines the methods and data formats that one program can use to talk to another.

Still feeling a bit abstract? Here’s a real-world comparison – think of an API like a power outlet. 

You don’t need to understand how electricity is generated or how your home is wired to plug in your phone charger and get power. The outlet provides a standard interface that allows many different devices, such as chargers, TVs, and laptops, to connect and get what they need.

Similarly, an API is a standardized access point that allows software programs to “plug in” and use another system’s features or data, without needing to understand how that system works internally.

How Do APIs Work? 

Every time you interact with an API, a simple process takes place:

  1. You (the client) send a request.

  2. The API receives your request and passes it to the server or service it connects to.

  3. The server processes your request, gathers the needed data, or performs the requested action.

  4. The API then sends the server’s response back to you.

This is the core idea of any API interaction: request → process → response.

Here’s an example that most people are familiar with, at least on the user end: shopping for a flight.

  1. You search → API request sent to airline databases.
  2. The APIs collect live availability from multiple airlines.
  3. Results are compiled and displayed to you in seconds.

There’s more happening behind the scenes than what’s described here. In the following sections, I’ll provide a more detailed explanation of the request, process, and response sequence. 

API Requests: What’s Actually Sent?

When you request information from an API, like flight details for a specific route, your application sends a structured message to the API. This message is typically made up of a few key components:

  • An endpoint – This is the specific URL that the API uses to access the requested data. For example:
    https://api.traveldata.com/flights?from=JFK&to=LAX&date=2025-06-10
  • A method – This tells the API what kind of action you’re taking. In this case, you’re asking to GET flight information.
  • Authentication – Many APIs require a unique API key or token to verify your identity and grant access. This helps prevent misuse or unauthorized access to data.
  • Parameters – These are extra pieces of information added to the request to refine your results. In the example above, the parameters include the departure airport (from=JFK), destination (to=LAX), and the travel date (date=2025-06-10).

So, if you’re building a travel website and want to show all available flights from New York to Los Angeles on a specific date, your system sends a GET request with those details to the API. The API then returns only the relevant flight options based on the criteria you supplied.

This process happens in real time, and users never have to see the backend mechanics. They get results.

Common API Methods (aka HTTP Verbs)

APIs use specific request “methods” that describe the action you want to take. Here are the most common ones:

  • GET – Retrieve data
    (e.g., “Get me the current weather for New York”)
  • POST – Send new data
    (e.g., “Submit this new blog post to my website”)
  • PUT – Update existing data
    (e.g., “Change this user’s email address”)
  • DELETE – Remove data
    (e.g., “Delete this comment from the database”)

These methods follow the same principles as websites do when loading pages or submitting forms.

API Responses: What You Get Back

Once the API receives your request and the server processes it, it sends back a response, typically formatted in JSON (JavaScript Object Notation). JSON is easy for both developers and machines to read and work with.

If you were searching for flights from New York (JFK) to Los Angeles (LAX) on June 10, the response might look something like this:

				
					{
  "flights": [
    {
      "airline": "Delta",
      "flight_number": "DL2045",
      "departure_time": "2025-06-10T09:00:00",
      "arrival_time": "2025-06-10T12:15:00",
      "price": "$249"
    },
    {
      "airline": "American Airlines",
      "flight_number": "AA1032",
      "departure_time": "2025-06-10T11:00:00",
      "arrival_time": "2025-06-10T14:25:00",
      "price": "$261"
    }
  ]
}

The app or website can then take this structured data and display it however it likes – listing flight times, prices, or allowing users to filter by airline. The API just delivers the data; how it is displayed and used is up to the application.

The Different Types of APIs

Not all APIs are created equal. Depending on who can use them and how they’re built, APIs fall into different categories. Understanding these types helps clarify how companies structure their technology and how developers (and businesses) interact with them.

Here are the four main types of APIs:

Open APIs (Public APIs) 

Open APIs are publicly available to any developer or business. They’re designed for widespread use, typically with simple documentation and easy onboarding. These APIs are great for startups, app developers, or anyone looking to build functionality quickly using external data or services.

Partner APIs

Partner APIs are only accessible to specific partners and require some form of permission, licensing, or onboarding. They’re not publicly available and often involve a contractual agreement. Partner APIs enable businesses to collaborate and share data securely without opening up systems to the general public.

Internal APIs

Internal APIs are used only within a company. They connect internal systems, departments, or services to improve operations, automate workflows, or streamline communication. Consider the e-commerce companies you shop with – each likely has an internal API to connect its inventory management system with its shipping system, allowing for automatic order fulfillment.

Composite APIs

Composite APIs combine multiple API calls into a single request. They’re often used when one action triggers a chain of events that would otherwise require numerous separate requests. Composite APIs can improve performance and user experience by reducing the number of server requests, which is especially important for mobile apps and time-sensitive tasks. 

For example, travel booking apps or websites could use a composite API to fetch flight options, customer loyalty points, and upgrade availability in one go, instead of making three separate requests.

Each type of API serves a different purpose, but they all function on the same core principles: structured communication, security, and efficiency.

Getting Started with APIs 

Curious about APIs but not sure where to begin? No worries at all! You definitely don’t need to be a full-stack developer to start exploring what they can do. Whether you’re interested in using them for a personal project, your business, or even to help with SEO, here are some simple, actionable ways to jump right in.

Simple, Well-Documented APIs to Explore

The following are APIs that are easy to understand and have thorough documentation. They even have a “sandbox” or demo you can play with.

Great beginner-friendly APIs:

Use an API Testing Tool Like Postman

Postman is a free, visual tool that lets you send API requests without writing code. It’s perfect for learning how endpoints, parameters, and responses work.

What you can do with Postman:

  • Enter a URL (endpoint)
  • Choose a method (GET, POST, etc.)
  • Add headers or parameters
  • View the returned JSON response

Using this tool provides a way to learn the mechanics of how requests are structured and what kind of data comes back.

Try a No-Code Integration Tool

You can use platforms like Zapier or Make to connect APIs without writing a single line of code. These tools let you automate tasks by linking apps via their APIs.

Have Fun Exploring the World of APIs!

A little curiosity and hands-on exploration can go a long way – and before you know it, you’ll be confidently using APIs to power smarter content, better automation, and deeper insights.