Where can I learn how to use APIs online?

Start with HTTP basics: requests, responses, methods like GET and POST, status codes, and JSON. The MDN Web Docs have beginner material on HTTP and using the JavaScript Fetch API.

After that, pick a service with an API and work through its official getting started guide. Pay attention to authentication, the request format, and the response fields. Those are the pieces you'll need to connect it to an app.

For an AI service, go straight to the provider's API documentation once you know the basics. Look for a quickstart in a language you use, then try a simple request and inspect the response before wiring it into a page.

Keep your API key on the server rather than putting it in browser code. Provider docs should also explain authentication, usage limits, and pricing.

Try building a tiny API yourself. Make a backend endpoint that accepts a message and sends back a response, then use JavaScript to send a form submission to it. Seeing both sides makes requests and responses much less mysterious.

Once it works, write a short description of the endpoint, the data it expects, and what it returns. That will also make other people's API documentation easier to read.

One bit of terminology that helps: an API isn't always a web service. Libraries, operating systems, and databases also expose interfaces for other software to use. Web APIs are the right place to start for your app example, though.