Adjusting brakes on a car is a simple procedure that will improve the stopping distance of your car. Disc brakes adjust automatically every time they are used. Most drum brakes are designed to adjust when you drive in reverse and come to a stop. This isn't to say that drum brakes don't need to be adjusted occasionally.
The only time you would need to adjust disc brakes on a car is when they have been changed or any time the caliper has been removed. To adjust disc brakes all you need to do is pump the brakes a few times with the engine off, start the engine, pump the brakes a few more times, and then make a few stops with the car. The disc brakes are now adjusted and will remain that way through normal use.
Drum brakes are a little more in depth to adjust but can still be done easily. Jack the car up and support it on jack stands. With the wheels still on, spin the tire and see how many revolutions it makes before it stops on its own. The tire should spin between one and a half to three full rotations. The more drag you put on the drum the less the brake pedal will travel when stopping the car. This also can reduce the life span of your brake shoes and the drums.
To adjust the drum brakes you need to locate the cutout on the backing plate that gives you access to the brake adjuster. The cutout normally has a rubber plug in it that you have to remove. Once you have removed the plug you can insert a flat-head screwdriver into the hole to push the lever holding the brake adjuster in place away from the adjuster. Now you can insert a second screwdriver to move the adjuster. After a few turns on the adjuster spin the wheel again and see if the wheel spins more freely. If so you need to spin the adjuster in the other direction. After a few rotations of the adjuster you need to center the brake shoes. You can do this by pulling on the parking brake cable by the backing plate.
Once you have the brakes adjusted to your liking engage the parking brake and push the brake pedal to the floor. Now go out and check to ensure that both wheels are holding with the parking brake applied. If one of the tires is holding and the other is not you need to adjust the parking brake cable where it splits into two cables. Once you have the brakes and the parking brakes adjusted to your liking release the parking brake and make sure the tires spin again. Lastly don't forget to put the rubber plugs back into the cutouts.