Well after a simple search I have determined this new aquarium of mine came complete with an underwater filter. I am have no idea what it's good for, or if it's even needed for my sorority. I was hoping someone could tell me a bit more.
It's something like this. http://www.aquariumguys.com/undergravel4.html
It sounds like your tank came with an UGF, or undergravel filter. They're very good filters but a little more maintenance than hang-on-back filters. I know they're not good with planted tanks because the roots of the plants can quickly grow and clog the filter; also sand can get underneath and clog them. If your tank came with the AquaClear 30, I would use that instead.