The SPice10214 can handle 3 external potentiometers. The above picture shows one typical potentiometer attached to the P3 connector.
When the potentiometer is turned fully clockwise the wiper (purple wire) ends up at the "orange" end. In this position the board will return an analog reading at or very close to full scale. When the potentiometer is turned fully anti-clockwise the wiper (purple wire) ends up at the "brown" end. In this position the board will return an analog reading at or very close to full zero.
The P1 and P2 connectors work in exactly the same way.