How do you bleed an air brake lines?

Have someone sit in the car and pump the brake pedal. After pumping a few times, tell them to hold the petal down until you tell them to let up. While they hold the pedal down, loosen one of the bleed nipples on the brake cylinder or caliper. This will allow compress air to exit until fluid jets out. Close the bleed nipple after the pressure is released. Once the nipple is closed, your partner can resume pumping the pedal. Repeat this process on all the brake cylinders until there is no air left in the system and the pedal is firm. Be sure to check the fluid levels on the master cylinder often. It will lower as the fluid is forced in to the lines.