Drum brakes essentially work the same as disc brakes, which is by applying pressure. The difference is the working mechanisms are encased inside. As with disc brakes, drum brakes rely on the whole system to function properly to produce the desired result, which is to stop or slow down.
Brake drums are generally made of a special type of cast iron that is heat-conductive and wear-resistant. It rotates with the wheel and axle. When a driver applies the brakes, the lining pushes radially against the inner surface of the drum, and the ensuing friction slows or stops rotation of the wheel and axle, and thus the vehicle. This friction generates substantial heat.