The two characters: client and server

Almost everything on the web is a conversation between two roles.

• The client is the thing that asks. Most of the time that's a web browser — Chrome, Safari, Firefox — running on your phone or laptop. It's the customer walking up to a counter.
• The server is the thing that answers. It's a computer sitting in a data center somewhere, running all day, waiting for requests. It's the kitchen behind the counter.

The client never does the server's job, and the server never does the client's. The browser asks, "Give me the home page." The server replies, "Here it is." That's the whole relationship. A server is not a special kind of magic box — it's just an ordinary computer whose job is to wait for questions and send back answers.

One more word you'll hear constantly: request (the question the client sends) and response (the answer the server sends back). Keep those two words handy; they're the backbone of everything below.