The Potentiometer module uses a potentiometer, a variable resistor that allows you to adjust the amount of power coming out of the wiper output. You can use it to adjust power to anything including LEDs, buzzers and motors. 

Tech Talk

The potentiometer divides resistance by splitting a single resistor into two parts.  When the dial is turned, it is moving a wiper along that resistor. The wiper is splits the resistor at that point, changing the resistance between each terminal and the output at the wiper. The resistance between node 1 and node 2 always remain the same, and is equal to the sum of the resistance between node 1 and the wiper and node 2 and the wiper. Having the ability to divide the resistance also allows you to divide voltage and current, giving you control over the power supplied to parts of your circuit.