Often in Internet computing, you will encounter the terms "client" and "server." The Internet uses what is called a client / server model of communication. This is how it works:
Tim goes into a drive - through restaurant. He sees a big menu full of choices. He chooses a "big fun cool wacky meal," and informs the little speaker of his decision. He hears a tinny little voice confirm his request, then tell him how much it will cost, then tell him with a slightly bored expression to drive up to the first window. Presumably as he drives around the restaurant, some kind of food preparation is happening inside. He gets to the window and exchanges his cash for the food, then drives off.
In this illustration, Tim is the Client. He makes requests and gets stuff back. the restaurant is the server. It sits around waiting for requests from clients, processes them, and gives the results to the clients.
Most of the software that is designed to be used via the Internet is classified as client software or server software. Client software is designed to be used by ordinary users. Web browsers, email programs, ftp programs, and most of the other Internet programs you will interact with as a user are clients. The servers are the big Internet computers and programs which are set up to interact with clients. They generally have information designed to be read by various clients. For example, the web browser program you interacted with earlier was a web client (to be more precise, an HTTP client.) Let's say you used this program to go to the WhiteHouse at http://www.whitehouse.gov. When you place the url in the little box and tell the browser to go there, it tries to find a server at that address. The white house has a computer (sadly, it might not really be in the White house, but let's just pretend it is!!) with all the pages of the white house web site, and the appropriate programs to communicate those pages to your browser. The white house is acting as a server. (I guess that is somehow appropriate!)