To stop the vehicle, brake linings rub against the brake drum. This action creates friction, converting the vehicle's forward energy of motion into heat energy, which stops the vehicle’s tires. If the tires have traction, the vehicle will come to a stop. The heat is absorbed and dissipated into the atmosphere by the drums and linings.
The action of dissipating the heat into the atmosphere is the same as an air-cooled small engine, like that on a lawnmower or motorcycle. The fins on the side of the engine provide more surface area for the air to flow over and pick up the heat and dissipate it into the atmosphere.
Brake drums, and the rim of the tire to some extend, dissipate the heat of the brakes into the atmosphere in a similar manner.