The HTTP Protocol
An HTTP connection is a simple network socket connection. The Web server usually listens for incoming connections on port 80. After the connection is established, the browser sends a few lines of text indicating which Web page it wants to see, some request headers telling the Web server which kind of browser is making the request, and a few other interesting items.
The only part of the request that is required is the first line, which tells the server what file the browser wants. The rest is optional. Each line in the request is a human-readable text line, separated by a newline character. The request header ends with a blank line. The protocol is so simple, you can even interact manually with a Web server using the telnet