As a first step, you'll want a terminal on your Pi. There are a variety of options, explored in more detail in the Getting a Terminal on Your Raspberry Pi section of our introduction to the command line:
Since this project uses the GPIO pins for its own purposes, you'll want to choose between working directly on the Pi (this is fine if you're already set up!) or connecting via SSH (a good idea if you don't have an extra monitor / input devices laying around, and want to work from the comfort of your desktop or laptop).
Examples here will assume a working Raspbian installation with an SSH connection. Not sure how to get started?
For installating Raspbian, check out our guide to preparing an SD card for the Pi. If you need help finding the Pi on your network and connecting to it, check out our Pi Finder utility.
...and here's our guide to using SSH.