What are Versions?
Every time you sync your Draft to a project, a new version is created.
Each version has a number (for example Version 1).
When visiting a project page, the designs that are shown are of its "Live Version".
You can always rollback the live version and in that way control which version everyone sees.
How to Rollback
Go to your Project Settings by clicking on the gear (three dots) in the top right corner -> Project Settings.
Go to the Versions tab.
Click Set as Live next to the version you want to set as the Live version.