The internet allows many computers to talk to each other in a variety of languages.
One of these is HTML, the language of the world wide web.
Another is FTP, which is a way to transfer files back and forth.
Yet another is telnet, a command line client.
Clients and servers are the two types of computers on the internet. When you connect to your ISP and then start up a web browser such as Internet Explorer or Netscape etc.. to get on the web, your computer is a client. Technically, the web browser is the client but the difference isn’t too important unless you want to use two browsers for surfing the web. The computer you’re connecting to is the server.
For example if you go to Yahoo or Ebay, then your computer is connecting to one of Yahoo’s servers or one of Ebay’s servers.