A privilege is like a permission. In Celoxis, if you want to view an item like project or task or perform any action on it like edit or delete, you will need the corresponding privilege. E.g. to view a task, you will need the Task > View : Granted privilege, to delete a project, you will need the Project > Delete : Granted, while for logging time for another user you will need the Time Proxy : Granted privilege. If you do not have the privilege, you will not be allowed to perform the action.
Celoxis has a very granular privilege structure — with over 50 privileges, you get fine-grained control over user actions.
Some actions like creating users, require administrative privileges. Any user can be given admin privileges. To do that, login as admin, edit the user and check the Administrator Privilege under Access Control. Users with the administrator privilege can peform any action even if they have not been granted privileges explicitly.
Privileges are assigned to roles. Read the next chapter to understand the interplay between privileges, roles and users.