A potentiometer is a useful device used to represent a wide range of resistance. Just simply adjusting it, we can know a wide range of resistances in a circuit from anywhere near 0Ω to the specified resistance rating of the potentiometer. For instance, a 5KΩ potentiometer can be adjusted to give the resistance range from almost 0Ω to 5KΩ by adjusting the potentiometer knob.
Potentiometers are widely used in circuits, because they can increase or decrease the gain of a signal in a circuit. That means when the resistance of the potentiometer is decreased, the gain of the signal increases; or when the resistance is increased, the gain of the signal decreases. And the function can be used in circuits to control volume levels, such as the speakers, microphones.