You should assign a security level to a user. Those security levels control the visibility of certain objects in Xpert-Timer. You find security levels for projects, clients and documents.
Example:
A user owning the security level "Confidential" has access to all objects. A user with the security level "High" will see all objects with the security level "High" and lower, but will not see the objects of the security level "Higher" and "Confidential".