There should be three chambers. The first is a tall thin chamber that has a hole drilled into it and a 90degree elbow pointed up. Hook up the outflow from your tank to that. Also in the first chamber is a space for the built in protein skimmer/pump. In the second chamber, you need to first lay down the white eggcrate (the plastic checkerboard of 1cmx1cm squares). Once in place, stack the bioballs on top until full. Now, there should be a white plastic sheet with blue sides. Put that on the second tier and put the mesh filters on top. Add the cover to the second chamber. The third chamber is for a return pump.
With all that said, my recommendation is not to add the bioballs/mesh, especially if you are ever going to get into corals. It will serve as a nitrate factory and you will forever be struggling with water parameters. I wound up gutting mine and using it as a sump for a euroreef and pump for a calcium reactor.
I STRONGLY recommend that if you don't know exactly what you are doing with this setup by asking more people here! I set up my 90g without much of a clue and going on some bad advice and I regret the way that it is done (too late to fix once running). With a 180, a year from now you don't want to find out all the set up tricks. I'm sure that if you entice some people with free beer and pizza they would be glad to help you out!
Good luck!!!
Eric
