Third generation consoles have a reputation for overheating – it was the leading cause of the Red Ring of Death in earlier X-box 360's – so a cooling system is a good idea.
This unit goes between your X-box and the power supply: it plugs directly into the power socket on the back, and the power cord plugs into the cooler unit.
My main problem was getting everything plugged in. It was a very tight fit getting the unit plugged into the back of the X-box, and again for getting the power cord plugged into the cooler unit. But once everything was plugged in, there were no problems. It only turns on when your X-box is on, and the three fans aren't noticeably noisy (especially when compared to the X-box itself).