To clarify, downforce is produced when the weight of the air moving around the vehicle outweighs the vehicle itself. This means that a car is moving so fast, that the air in front of it and around it creates a gravitational pressure, measured in Gs. While air resistance may not seem like a good thing, in the Formula 1 world, it’s useful.
Downforce helps a Formula racing vehicle corner at high speeds, and also helps the vehicle to reduce wear on the tires; the tread is slowly worn down as the frontward spinning wheels grip the asphalt surface of the track.