The circuit above shows the connections for hooking a potentiometer to a Circuit Playground Express board. The center terminal of the potentiometer (the wiper) is connected to pad A1 although it could also be connected to pads A2 through A7. We tend to skip A0 as that is the analog output pin for sound and many potentiometer projects are related to sound for volume control, varying the tempo, and other sound-related features.
The value of the potentiometer is not crucial. The part suggested is the Adafruit 10 kilo-ohm (KΩ) model but other values should give similar results. It is suggested avoiding under 1000 ohms and over a mega-ohm to get the current flow in a good range. If you decide to use a breadboard instead of alligator clips, most Adafruit potentiometers are breadboard friendly (look in their description to make sure).
See the last page on what types of potentiometers are available out in the wild if you have specific requirements.