Anywho I got a bike and I notice that the rear sprocket has come loose and wobbles when I ride it, not allowing the chain to stay on. I also notice that there is some sort of ring shaped peice (a washer I suppose) that is visible and slides. Sometimes the sproket spins but the rear wheel doesnt spin. Is there any way I can fix this?
From your description "Sometimes the sprocket spins but the rear wheel doesn't spin", sounds like you may have a bad freehub. If the cassette was just loose on the freehub, the wheel should still be driven. Check out parktool.com , lots of good repair and maintenance advice there, along with good pics. The freehub can be replaced (or tightened-but if you've been riding it that way, could be damaged). Stop riding the bike until you get it fixed-could lock up at the wrong time.