A brake is a mechanical device which inhibits motion. Its opposite component is a clutch. Brake pedal slows a car to a stop. When you depress your brake pedal, your car transmits the force from your foot to its brakes through a fluid. Since the actual brakes require a much greater force than you could apply with your leg, your car must also multiply the force of your foot.
The brakes transmit the force to the tires using friction, and the tires transmit that force to the road using friction also.