Single pole three toggle switch
You never switch a neutral

That principle should make it clear how this should get wired. Based on your picture, this diagram should help:



You take the hot (typically black) wire from your breaker, connect it to the single black screw on the set of switches. The black screw indicates it's the "Line Side." You take a bunch of wires and connect them to the silver screws (which indicate "Load Side"). Those wires then go to their respective connections at the light/fan/heater. There should be a single white wire to pigtail to, which is your neutral return. That should not be switched anywhere. You probably also have a chassis ground on your light/fan/heater. Be sure to wire that.