Start at the foundation every API is built on. Learn what an API actually is, how the HTTP request/response cycle works, and the meaning of methods (GET, POST, PUT, PATCH, DELETE), status codes (200, 201, 404, 500), and headers. Then understand the REST style itself: resources, statelessness, and why REST became the standard for connecting apps. By the end you can read and understand any HTTP exchange.

A good API is easy to read and predictable. Learn to model your data as resources and name endpoints well (nouns not verbs, collections vs single items), use path and query parameters correctly, and handle real-world needs: filtering, sorting, pagination, and versioning. See what separates a clean, professional API from a confusing one — and design URLs other developers love to use.

APIs exchange data, and on the web that data is almost always JSON. Master JSON syntax (objects, arrays, types), how request and response bodies work, and the role of the Content-Type header. Learn to validate incoming data, shape consistent responses, and return clear, useful error messages when something goes wrong. By the end you can confidently move structured data in and out of an API.

CRUD is the heart of almost every API. Learn how the four basic operations — Create, Read, Update, Delete — map onto HTTP methods (POST, GET, PUT/PATCH, DELETE) and the right status code to return for each. Build endpoints that add new records, fetch single items and lists, update existing data, and delete safely. Understand idempotency and PUT vs PATCH so your API behaves correctly every time.

An open API is a risk. Learn the essentials of protecting one: the difference between authentication and authorization, securing requests with API keys and Bearer tokens (a first look at JWT), and why HTTPS is non-negotiable. Then cover the everyday defenses every API needs — rate limiting, CORS, and avoiding common mistakes that leak data. Finish able to ship an API that is safe for real users.