When you take the train from Munich to Nuremberg you might want to buy a so-called "Bayernticket". It costs 30 EUR and up to 5 people can use it, I think you can even use public transportation in Nuremberg and Munich with it. However, you can only use the "Regional Express" train from Munich to Nuremberg which is a little slower, but not much. In Nuremberg there'll be lots of other young people with backpacks and sleeping backs and beer: Follow them. The train to the festival (S2 or S3) leaves near where you arrive in Nuremberg.