Desktop computer cases are the home to all the computer components. Everything including the motherboard, the hard drive, the cd drive, the floppy drive and the power supply go inside a computer case.
Computer desktop cases generally have trays for the CD/DVD drives, floppy drives and hard drives. There is also a place for the power supply and the on-switch cables which usually come with the case. These are connected with the buttons at the front and these connect to pins on the motherboard.
When placing your hard drive or CD drive into the motherboard try to keep as much space between them as possible. If they are too close there is more chance they will overheat. A good computer case also has a few fans circulating the perimeter of the case. These either connect to the motherboard or to the power supply and they keep the computer much cooler.
A few years ago, desktop computer cases were just plain. However, today for a little bit more money you can get computers with cool designs and colors. Some computer cases now come with front USB (Universal Serial Bus) and some even have a card reader, firewire or ports for a headset.
These extras can be very handy as you won't need to reach behind the computer to connect devices. This guide on how to choose a computer case will help you choose that case that is right for you and your needs.