Click the Current Task -> Categories... menu item.
For each category that should be available for the user, click the Permissions tab to specify which users can view, create, delete or edit tasks. To view a task, users should be able to view all parent tasks.
Click the Current Task -> Workflows... menu item.
Click the Message Types tab.
For each message type, click the Permissions tab to specify which users can create and view messages of that type.