the black box in the corner of the tank is an overflow box. there are holes in the bottom of that box where you will attach tubing that will head to the sump, and a smaller tube will return water to the tank.
i don't know what those pumps were used for but it seems they have venturi's on them, which mix air and water. you would use something like that on a protein skimmer, but it looks like one wasn't included.
you will need a pump strong enough to return water from your sump which will be below in the stand i guess, to the display tank.