A server is really nothing more than a big computer. However, unlike most, they do not have the usual accessories like a monitor and keyboard.
Servers house data, most for websites although they can be used for company files. They are tied to a network meaning they can be accessed from multiple locations. This is usually done over the Internet.
Basically, servers interact with other computers instead of humans.
Servers are accessed based upon their IP address. Most users are not aware of this since they simply type the URL into their web browser. This, however, is translated into the Domain and File Names so that the server can be located.