A real development environment.
Web-based so you can connect to it from anywhere.
The editor should, however, be familiar.
Github is spinning up a virtual computer in their data center that is connected on one side to your Github repository and on the other to a development environment that runs in your browser.
It may take several minutes to open up the first time.
When your codespace is open, at the bottom left there is an indicator of what branch you are on.
You can also click on it to get a menu to switch to a different branch.
You will use this to switch branches.
Close the Codespace tab when you’re done.
You can use the same Code menu later to reconnect.