A version is a full copy of the page tree. Use versions when your product has releases that need different documentation, such as v1 and v2.
The default version
One version is the default. Its pages live at the root of your site:
https://docs.example.com/getting-started (default version)
https://docs.example.com/v1/getting-started (version "v1")
Readers switch versions with the version menu in the top bar. When the same page exists in the other version, the menu links straight to it.
See Versions for how to create and manage them.