URLs identify the protocol to be used, server to be accessed, and filename or document to be received and displayed. Every document, file and image on the World Wide Web has a unique address. When you select a URL, your browser interprets it and starts an appropriate session on a specified server. The URL must be typed exactly as noted. Typos will get you an error message.
Servers store information and process requests from clients.
Servers send instructions to the client on how to display all this information. HTML is a simplified derivative of SGML, or Standard Generalized Markup Language, which is a code used to make documents readable across a variety of platforms and software. The browser you use knows how to convert the HTML pages it receives from Web servers into recognizable Web pages, and not just a lot of strange looking symbols and characters on a page. Unlike HTML, it is not a fixed format and users can define their own customized markup languages for many classes of document. Users navigate the World Wide Web through the use of hypertext links.