Brake pads are equally crucial auto parts that are necessary for the brake's function. Brake pads are the auto parts that take the brunt of the force necessary to stop the car. In a disc brake system the pedal will activate a hydraulic line which will squeeze calipers against the brake rotors. Brake pads are positioned between the calipers and the rotors so that the calipers are not gripping directly onto the brake rotors. These are also important to be able to absorb that amount of energy and heat and thus stop the car.
If you have a multi-gear bicycle then this can help you to understand how brake pads work. Here the grip on the handles is the equivalent of the brake pedals and when you squeeze the grip, the two calipers are squeezed together over the bike tire.