Some bicycles have coaster brakes, which are applied by backpedaling, but most have hand-operated caliper brakes. Caliper brakes may be either center-pull or side-pull brakes. The difference is mainly in the entrance of the cables into the brake mechanism.
With either type of caliper brake, the pads should contact the rims of the wheels, not the tires. If they don’t, loosen the nuts that secure them and adjust their position in the slots of the caliper arms, then retighten the nuts.
Brake pads should clear the wheel rim on each side when the hand levers are fully open. When squeezed, the levers should be at least 3/4 inch from the handlebars when the bike stops. If the pads or levers need adjusting, squeeze the pads against the wheel rim by hand. Use a wrench to loosen the locknut on the adjuster screw, and turn the screw by hand-turn it counterclockwise to bring the pads closer to the wheel rim and clockwise to move them farther away. Tighten the locknut and test the brakes.
If the levers or pads are still out of adjustment after the adjuster screw has been turned as far as possible, the cable is slack. Loosen the anchor nut and have a helper hold the pads against the wheel (or use a C-clamp to hold them). Using pliers, pull the free lower end of the cable to take up the slack. While holding the cable taught, tighten the anchor nut. Release the pads and recheck the adjustment.
The pads on side-pull brakes sometimes become stuck in the closed position. Loosen the pivot bolt just until the pads come free but do not wobble.
If side-pull brake pads are not equidistant from the wheel, tap the spring on the more distant caliper with hammer and screwdriver until the pads are balanced. If the center-pull brake pads are not equidistant from the wheel, use an adjustable wrench to turn the yoke across the tops of the caliper arms in one direction or the other to bring the pads into position. Be sure that the anchor nut is snug.