VisNZ that is an Under-gravel filter, the piece in your hand slides into the piece near the top of the pic.
Make sure that the fatter of the two pipes is furtherest from the glass, cuts down on the noise.
The airline fits onto the smaller of the two pipes.
EDIT:- just noticed, you are missing a smaller pipe that fits into that foot thing and that in turn, fits into the airline from the airpump
The other is a canister, internal filter.
Remove the blue top by twisting it, plug in the power and have a look into the hole on the underside.
You should see a thing like a propeller, give it a flick with your finger if it doesn't turn over and start whirring, you are prolly in trouble.
Alan 104