Hi Elly, you've lost the alternator belts, they are the belts that are on in this picture:
They go from the main crank pulley at the bottom, around the alternator on the left, which recharges your batteries etc, and around the fan (missing in the pic) thats why the fan doesnt turn. The fan, then has a belt on it which goes to the power steering pump, which would sit top left in this pic if it was there. Because the fan isnt moving, you have no power to the steering and its heavy.
Normally on a delica its 2 belts for the alternator. They are a pain to put on as its awkward, and my advice when they are on is always tighten them, run the engine for 10 minutes, let it sit overnight, and tighten again, since they always seem to need tightening a week later if you dont!