How does a biowheel filter work?

Hello everyone!

I've just decided to convert my old saltwater tank to a freshwater tank. I own most pieces of equipment that I'll need, but I'm having trouble with an biowheel filter I had lying around. I've never used it before, and don't have any instructions. It's all plugged in ready to go, but doesn't seem to be sucking up any water.

How does it work exactly? And how will I get it going?

Thanks alot!

that was so simple! Thanks for the tip