The two end terminals - are the ends of the resistor (maximum resistance)

You would normally connect to either, the left terminal and the middle terminal

OR the right terminal and the middle terminal - the middle terminal connection slides along the resistor as you turn the pot - altering the resistance.

Depending on which combination you use - would alter which way you turn the pot to increase or decrease the resistance -IE clockwise or anticlockwise.

The end terminal which is not used is connected to the pot body and earth to stop Hum on guitars