Lol I hope your time at camp is fun!
A BETA is someone who plays music for you while you write.
Haha just kidding. BETA's are really great! I use my best friend (who is a MAJOR grammar nazi) as mine.
As RyanCyandieKiller said, they edit your stories. They are also good for helping you with ideas and writing your story if you get stuck in a rut.
You can pretty much go to then for anything related with your story(ies) :D