Air gets trapped inside the brake lines. They become mushy because the fluid that is needed to push the brake pistons is low, and eventually they will fail. Bleeding your brakes makes sure that there...
1. Begin at the corner furthest from the driver and proceed in order toward the driver. (Right rear, left rear, right front, left front.) While the actual sequence is not critical to the bleed...
open the bleeder valve on the brake calipers and press the brake pedals you need 2 people for this job or you can go to your local auto parts store and buy a brake bleeder kit for a couple of bucks...