User Manager is only available to Administrators.
Think of Workspace as the live project management section of the Platform and Schedule Manager as the brains. In order for a task to become a live piece of work to be reported on, it requires user assignment. After all, what's the value of a task if there's no one responsible for it.
Schedule Manager and User Manager work hand-in-hand. You can set up a schedule without users, but remember that in order for the system to activate Tasks require user assignment.
To access User Manager select a project then select Admin Tools. From the Admin Tools dropdown menu select User Manager.
With users added to the project you can now assign them to Tasks via Schedule Manager.
At this point, you've just completed the basics of User Manager.
With an understanding of Schedule Manager and User Manager, you can now effectively command the Harbr Platform and put your project management on auto-pilot.