As has been said, you start at the bottom of whatever seniority list you are joining. If you have the required time to be Captain, and they can't fill classes from within you may start out as a Captain. This happened a few years ago with Pinnacle. There was about a six month period where nearly every class had new-hire Captains even though about 600 FO's were senior to them. In order to address this, Pinnacle did what most companies are doing, no one to fill the cockpit?, well, let's just lower the mins for that position and voila, lots of new Captains.