the inlet and outlets should be labeled on your ocean clears and the best set up is to have the pump after the canister, especially if you have sand in your tank.
You need to put the pump first and that will go to the upper 3/4" hole. The return from the pump is the lower 3/4" hole on the other side. Your going to have two more openings on the front of the filter. The top smaller one is for a pressure gauge or just plug it, the lower one is for a drain to drain the canister for filter changes. I have a couple of these filters and I love em.