TCX, this might help you:
Approach - Doesn't use radar to separate aircraft, provides procedural service to a/c inbound to or flying in the vicinity of an airfield. May however use radar derived information to provide information to pilots on potential conflictions.
Approach RADAR - Uses radar to separate, and vector a/c into a suitable position to make an approach to an airfield orfor handover to another controller
Director - Deals with the final sequencing of a/c making an approach to an airfield
Tower - Responsible for isuing landing, and take of clearance, responsible for a/c flying in the immediate vicinity of the airfield, responsible for all movements on the runway (including vehicles)
Ground - responsible for all a/c (and sometimes vehicle) movements on the ground
Delivery - Issues departure clearances to a/c on the ground
This is just a general guide to what each position does, different units allocate different responsibilities to the approach and radar positions, but essentially it's as I've said above