This was written while I was getting up to speed with Cubical Agda.
Quick start
Installing Agda
If you already have Agda installed, great.
If not, follow the official instructions.
I use brew install agda.
Installing cubical
There are install instructions at https://agda.readthedocs.io/en/v2.6.1/language/cubical.html .
Only the paragraph "For detailed install instructions..." is necessary; it amounts to cloning the Cubical repo, building it, and adding it to ~/.agda/libraries and ~/.agda/defaults.
Which file to start with
The first file is File1.agda.
Open it up in emacs (or your normal Agda editing environment) and follow it.