You can read how Permissions work in Redtail CRM here. You should note, however, that permissions work a bit differently for clients created or linked from ClientWorks to Redtail.
Redtail permissions are built to mirror ClientWorks permissions. For every contact that LPL sends to Redtail they send a corresponding Rep Id . If you have access to that specific Rep Id in ClientWorks, you will have access to that record in Redtail. If you do not have access to a specific Rep Id in ClientWorks, then you will not have access to those records in Redtail that are associated with that Rep Id. Please note that the database owner will have access to all contact records in Redtail regardless of Redtail or ClientWorks permissions.