This is a rotary variable resistor that changes its resistance with the pot position. Connect to one of the outer pins, GND to the other outer pin, and the center pin will give variable voltage between VCC and GND depending on the pot position. One use is to connect the center pin to an ADC to read inputs from the user, or can be used to change an LED brightness, or can be used in changing the PWM of a microcontroller. It is crucial component in many electronic circuits, and it comes with variable values.