If you plan to limit the visibility of your customers and projects through the workgroups, you must enable the workgroup mode for the entire Xpert-Timer. You do this in the administration program "XTAdmin". There you define the workgroup mode. Please read the chapter "Working groups".
In the tab "Workgroups" you can then, after activating the workgroup mode, assign the users to certain groups. These groups help with the organization of the employees and also act as filters in the evaluation module and the project assignment.
Just put a tick in the groups where the employee works. Use the Plus to add more custom workgroups.