The vast majority of bicycle brakes on commercially available bikes, such as cantilever brakes and V brakes, have very similar structures. They consist of two metal branches with some sort of pad on the end that is designed to press against the wall of the bike tires and thus slow it down and make it stop. Some bicycles also use a disc brake structure, but the technology for these has not quite caught up to the marketability of the cantilever brakes style.
Before V brakes appeared on the market, cantilever brakes were the standard type used for any touring or tandem bicycle that was designed to carry heavy loads. These brakes were most popular on road bikes primarily, but when mountain bikes first started to become popular, these elements were also use for them. The cantilever brakes were able to accommodate the wider tires frequently found on mountain bikes.
Cantilever brakes operate with the use of a straddle wire between the ends of the metal rods that hold the pads to the bike tire walls. When the person writing the bicycle squeezes the hand brakes, this wire is pulled evenly and the brakes close around the tire thus slowing it down.
These days, technology has marched on and V brakes and lightweight disc brakes are being used more frequently on all different types of bicycles: touring, road racing, tandem and mountain or off-roading bikes. Cantilever brakes are now found more often on lightweight touring bikes and ones designed for light recreational use.