Air Conditioners

I just moved to a new apt. and it has those openings in the wall for air conditioners. Am I supposed to put my window A/Cs in these?

I rather doubt that.. Of course I am not looking at that opening but I assume that the a/c unit you need there is "back vented" and not the window unit you may have used in another apartment. Check with the landlor or the management agent or whoever you are renting from.

usually those holes are for a particular a/c unit, and they're not that inexpensive. they do, however, keep your windows free to let fresh air in.

Those are designed for 'sleeve' type air conditioners.

The 'window' type air conditioners are designed to vent on the sides.