How http listening works

I am newbie in开发者_如何学JAVA network programming. Dear developers can you tell me what mean listen via http some URL. and in what form information must be on specific address (URL) for to be listen . For example we have HTTPListener class in C# and he has such things like Open and event for message receiving. how often he try to get information from URL . Please clarify listening functionality to me.

Thank you in advance.

There is a brilliant article on http://msdn.microsoft.com/en-us/library/system.net.httplistener.aspx