Brake pad misaligned - Realign a rear or front direct-pull cantilever brake pad if it is rubbing against a tire, hitting spokes, or not effectively gripping the tire rim (e.g., making a squealing sound). First, use an Allen wrench to loosen the bolt attached to the back of the brake pad (see first picture below). Second, engage the brake pad with the tire rim by squeezing the brakes. Third, align the brake pad such that it is centered on the tire rim and that the entire brake pad is making uniform contact with it. Fourth, tighten the bolt attached to the back of the brake pad maintaining desired alignment. Finally, test that your brakes are now working to your liking and that they are not rubbing against your tires, hitting spokes, or making a squealing sound.
Brake pad does not separate from tire rim - If a rear or front direct-pull cantilever brake pad does not retract away from a tire rim after releasing the brakes then the problem may be with the tension in the brake arm's spring. Tighten the tension in the brake arm by turning the tension screw clockwise with a Phillips screwdriver. Reduce tension by turning the screw counter-clockwise. The tension screw can be seen in the following picture as the small black screw at the base of the brake arm. In addition, it is recommended to clean the brake arm with WD-40 so that the brake arm can move freely.
Brakes are too loose or too tight - Front and rear direct-pull cantilever brakes can be loosened or tightened by adjusting the length of the brake cable. First, use an Allen wrench to unwind the bolt that pinches the brake cable. For loose brakes, shorten the length of the brake cable. For tight brakes, lengthen the cable. Next, tighten the bolt with your Allen wrench. Finally, test that your brakes are now working to your liking. It should be noted that front brakes provide most of your stopping power but you do not want to overuse them at high speeds such that your front tire locks up and sends you flying over your handlebars.