A dryer belt connects the dryer's drum to the drive motor, transferring the power to that drum and allowing it to turn. The usually slender belt wraps around the entire drum, a tension pulley and a special wheel on the motor. If the belt breaks, the drum doesn't turn.
A simple test is to reach into the drum and try to spin it. If it does rotate, chances are the belt needs to be replaced. Some dryer models do not even turn on if the belt is broken. The tension pulley opens when the belt breaks, which prevents movement. Also known as an idler pulley, this device keeps a steady pull on the belt, creating the needed friction to keep the belt in place on the drum and motor.
In some cases, the tension pulley causes squeaking noises, a sign that the belt is wearing out. It can also create a burning smell because the friction factor is out of sync, either from a broken belt or one that moved out of place.
The type of belt needed, and its placement, is determined by the dryer model. Most manufacturers, including Amana and Frigidaire, require that the groves on the dryer belt face the drum. Admiral and Magic Chef designed their machines so the flat side of the belt faces the drum.