NEWB NEEDS HELP AT FIRST SEALED DECK TOURNAMENT!!!

I am a new mtg player who has played mtg 2013 on steam and has causally played with a few pre constructed decks. My friend and I (both just casual) are going to our first sealed prerelease deck competition for dragon's maze. I apparently need to choose a guild and I have no idea how! I have about 12 hours to choose before it starts tomorrow morning so please help me and give me as much advice as possible! Thanks!