Colla pier is about 3km west of Schull village. The pier and the ferry departure point are clearly signposted. There is a carpark at the pier.
If you have SatNav the following links are useful:
For Long island: http://www.myloc8ion.com/index.php/maps/find_code8/?code=T77-70-F82
Zoom in and out on the maps to get an overall picture.