Drum brakes, found on older-model bicycles and tandems, are an older form of braking system for bicycles. They use the same concept that older cars with drum brakes use: a cable pulled tightens the hold of the drum on the braking axle. In bicycles, the braking axle is the centre of the wheel. The brakes are connected via cable to brake levers on your handlebars, just like any other bicycle. The adjustment process should take about five minutes depending on the adjustments needed.
Place your bicycle on the repair stand, and clamp it to the stand via the seat post. The bike stand is not absolutely necessary but makes it easier to perform repairs on your bike. This way, you don't have to worry about spinning the wheels and pedalling.
Spin one of the wheels and listen to the brakes. Depending on the adjustments needed, either tightening or loosening, you can hear and feel the adjustments needed. When spinning the wheel, if you don't hear brakes rubbing and the brake lever that coincides with that brake takes more than a 50% depression of the lever to stop the wheel, you need to tighten your brakes. If you spin the wheel, hear brakes rubbing and the wheel slows down quicker than normal, you need to loosen your brakes.
Tighten your brakes by following the brake cable to the outside shell of the drum brake. A small tensioner connects to the inside of the brake, which tightens the actual brake. The brake cable pulls this tensioner, thus tightening the brakes. Unscrew the bolt on the tensioner that holds the cable with the appropriate-sized Allen wrench. Remember to keep tension on the cable with your fingers or pliers and pull the cable slowly about two centimetres, then re-tighten the bolt to secure the cable back to the tensioner.
Loosen your brakes by doing almost the same process, only instead of pulling on the cable to tighten it, let it out slowly about two centimetres, or however far you need to, to stop the rubbing of the brakes on the axle.