In renting property, what do I so when having to pay taxes (not yet-spc)

I rent a room in some one's house that I live in through a web site . They with hold 28% if I do not give them my tax information. So far I've  made 16,000 plus. I don't know what to do . I've never payed taxes before. I've been away for some time . If you can guess what I mean .