What do people do to prevent their cars from rusting?

Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen.

The terms "rust" and "rusting" only mean oxidation of iron and its resulting products. Many other oxidation reactions.

The nature of rust changes with time, reflecting the slow rates of the reactions of solids.

Rusting is an oxidation reaction. The iron reacts with water and oxygen to form hydrated iron(III) oxide, which we see as rust. 

To prevent rust on a car, one should wash it every few weeks with soap, water, and baking soda to neutralize road salt and prevent sediment from wearing through the protective paints.