the USB ports on the side of the computer will have a plug on the end that will look like this...
this will plug into the motherboards USB headers. you will need to either look at the manual to find the USB headers, or you can look at the motherboard itself and it should say USB1,2 or 3,4 depending on how many USB ports you have (a single USB header actually holds two USB ports, so you will see two consecutive numbers.)