Body tuning involves adding or modifying spoilers and a body kit. Sometimes this is done to improve the aerodynamic performance of a vehicle, as in the case of some wings or bumper canards. More often, these modifications are done mainly to improve a vehicle's appearance, as in the case of none-functioning scoops, wide arches and the like. Very rarely does an aftermarket bodykit improve performance, the majority add weight and make the car handle worse.
The ECU or Computer is what controls every aspect and function of your car. Most cars built since 1992 and indeed many before that had a computer to monitor and manage the engine. Now with the addition of catalysts and fuel economy requirements the computer has evolved into a complex system.