Downforce

This is the most fundamental setup change- and one that almost anyone can understand. Increasing it will make your car go round corners faster, but go down straights slower. What you're doing is changing the angle of the spoiler on the back of the car. The steeper the angle, the more air it can deflect to push the car onto the tarmac, but this causes drag. Some track benefit from a minimum of downforce (Monza, for example) while others demand high settings (e.g. Vancouver, Laguna Seca.)