the first thing you must do is
learn socket programming. after you have searched for an intro socket tutorial/example, it is fairly straightforward if you know the protocol. therefore, after learning how to create/bind a socket (port 80), open it and listen for/accept connections, read and write to it (which should be similar to writing to other IO streams, like files), you must learn the basics of the HTTP protocol. the basics of the protocol would learning an example "GET" request sent from client to your server. there are many examples of this type of sample dialog of the HTTP protocol online.
give this a shot (starting with basics of sockets if you dont already know it, and then learning basics of the protocol) and post any code or questions you have. if you cant get the code for it, then post some pseudocode and we can help you translate it to your programming language, ie:
Code:
- create socket on port 80
- listen for connections on this socket
- when a connection is made, then [...]
