The code in this guide is written in CircuitPython. So, before proceeding, make sure you have CircuitPython and the latest libraries installed on your board.
If you are new to CircuitPython, read these guides first. They will explain how to install CircuitPython and the necessary libraries.
They also cover how to load and run code, access the REPL for troubleshooting, etc.
Adafruit suggests using the Mu editor to edit your code and have an interactive REPL in CircuitPython. You can learn about Mu and its installation in this tutorial.