"our automobile's brake system may be one of the most important safety systems in your vehicle. When you apply pressure to the brake pedal, the master cylinder forces brake fluid via the brake lines into the wheel cylinders or caliper pistons. This activates the brake shoes or pads, which rub against the rotor or drum, and this slows your car down. You should check and service your brake system every six months to keep it in working order."
Source : Wikihow