How do you sing in B-Flat?

I have an audition tomorrow (yes i know, shame on me) and I have no idea even what a key is! I haven't been able to practice with the recording because it was saved on the school's computer and I had no free time to go to the library. I'm supposed to sing the Judy Garland version of "Somewhere Over the Rainbow" in B-Flat (I think it's the low one....). Please help me!!!!!