Every time you are navigating on the internet, you are using the HTTP. Even when you are booking a ride on Uber, you are using HTTP. In fact, HTTP is present in almost all the applications that you use on a daily basis.

HTTP is based on the principle of client-server communication. It means that every time you want to access an information or resources, you have to send a request object and the server will send you all the requested information into a response object. The following diagram explains this communication:

So, in order to really understand how to design a robust HTTP RESTful API we need to know how URLs works and learn about the HTTP protocol.