The brake system in a vehicle relies on pressure in order to function properly. If there is a leak in any part of the system, fluid will escape and air will get into your brakes. When this happens, the brakes will become soft and mushy, and they may not stop your vehicle as quickly as they should. If the pedal is going almost down to the floor or has lost a significant amount of pressure since the last time you pressed it, you may need to pump the brakes in order to stop the vehicle.
Press down on the brake pedal quickly and forcefully. It does not have to go all the way to the floor, but the pedal needs to be pressed hard enough so that it moves noticeably.
Release all pressure on the brake pedal for a moment. Once the pedal has moved back up, quickly press back down on the pedal and release it again.
Continue to press down on the pedal and release it several times in rapid succession. This is what's known as pumping the brakes. You will want to continue pressing down and letting up as quickly as possible until the brake pedal feels firm and you are able to stop the vehicle.
