The computer case is what you put all your components inside. Computer cases come in all shapes and sizes, make sure you select a size you are happy with, Do you want a small case so it can fit under your desk nicely? Or do you want a big case so you can put more hard drives / CD-ROMS in?
Select A Case To Match Your Motherboards Form
The first thing you need to look for in a computer case is what motherboard forms it supports. When you selected a motherboard in the previous step the motherboard would of had a form, 99% of the motherboards you can buy are either ATX or micro ATX. Make sure the computer case you want to select supports this form.