Some Basics of a Potentiometer?
A potentiometer has 3 terminals. Let's call them A, B, and Wiper. They are constructed like this.

There are two resistance values of interest: Ra is the resistance between terminal A and the wiper. Rb is the resistance between terminal B and the wiper. The resistance between A and B is always the same no matter where the knob is.

When the knob is all the way toward one side, Ra is zero and Rb is the full resistance of the potentiometer. When the knob is all the way to the other side, Rb is zero and Ra is the full resistance of the potentiometer.

The reason they are arranged this way is so that Ra and Rb can be used to form a voltage divider whose ratio changes linearly with the position of the knob. "Voltage divider" refers to the circuit arrangement of two resistors. "Potentiometer" refers to the physical component.

I recommend you get a potentiometer and an ohmmeter and play around. It will become clear.