If you are using an office-style chair that has wheels on the bottom of it, you will use the chair wheel stoppers to prevent your chair from rolling around while you pedal your Cubii. The chair wheel stoppers are like coasters with pre-made divots that your chair wheels can rest into. Below are some helpful pictures that show how to use the wheel stoppers. For best results, try spacing out your wheel stoppers so that one is at your front wheel and the other is at your back wheel.
Here is a quick video to help explain!