This guide will show you how to interact with one of the Adafruit CircuitPython-compatible boards which feature analog I/O such as the Circuit Playground Express.
If you'd like to learn more about CircuitPython (not required for this tutorial) you can see this guide.
To see the CircuitPython REPL interactive environment and follow along yourself, Adafruit recommends the Mu Editor. With a board connected, you can clock the Mu Serial button to see the serial stream from a board. If you press a key, Mu woll start a REPL interactive session with the board like the code in this tutorial. Again, this is not required for this tutorial, but if you'd like to learn about Mu and look to install it, see this guide.