A server is basically hardware and software and protocol. We will go over these three basics of your hosting server.

Server hardware.

Server hardware is so similar to your old PC hardware that the price of server hardware has come down considerably. Down enough that it's tempting for a lot of us to host our own server. But that's a whole different article. All a server is:

Very fast processor.
A large amount of RAM.
A vast amount of Disk Space.
Connection to a T1 line (access to the outside world).

The hardware is housed in very large office buildings. There are many racks of servers filling these climate controlled rooms. Most of the server host brag of their 99% or better uptime. This is very impressive and another reason to use a server host. How often have you re-booted your PC in the past?

Software. (Operating system)

There different operating systems on the market. Most likely the software on your server is running Apache on Linux, an open source product. Servers need to be secured and an open source application is more likely to be less buggy and more secure then their larger competitor Microsoft. These servers use an interface for you to access and configure them, a control panel. Some control panels are more complicated then others. Depending how technical you are, this is a point of concern when picking a server host.