There is a timing mark on the block, just above the gear on the crankshaft. Match up the mark on the gear and you are at top dead center for cylinder 1. Match the camshaft gear marks at the top of the timing belt cover (between the 2 dots). Release the plunger to put tension on the belt. Turn the engine over twice and make sure the marks still line up (You could even start the engine for a minute of two and check the vacuum level to see if you got it right before reassembling everything).