If you are using Microsoft MakeCode or CircuitPython, you'll need to do a couple of basic things to set things up.
In Makecode, the editor is located at https://makecode.adafruit.com/
See this guide page from Introducing Adafruit Circuit Playground Express on setting up your CircuitPython environment.
Adafruit suggests using the Mu editor to edit your code and have an interactive REPL in CircuitPython. You can learn about Mu and installation in this tutorial.