I seriously need help with this whole Prom thing!?

So I am going to my first and probably last prom i'll ever go to in a few weeks and I have NO IDEA what i'm doing. I don't know about anything formal what so ever. I don't know how to rent a tuxedo, how much it will cost to rent it for one night, where to rent it, how to get fitted and where, can it be a same day sort of thing or do i need to do all this in advance... I don't know where to buy a corsage for my girlfriend or how much they cost or what kind or if it will match. I just don't know anything about prom and I feel as if i'm expected too! Time is flying by and I just wish there was someone to answer all my questions. haha. That's where you all come in? Please help me prepare for this one big night!