I have this exact thing. the pump goes in the left side of the box and the screws that are on the box hold it in place. the output of the skimmer goes into the right side of the box.
its purpose is so it only skims the top of the water where most the "junk" is so you want to place it as close to the surface as possible. the only problem with it is you need to keep your tank full almost constantly.
if you have any questions let me know since i have this exact product.