Yeah go in, train. If you like it then sign up. Don't have an ego, expect people to be more experienced than you, but don't let it frustrate/discourage you. Everyone has to put in the time if they want to be good. If you have questions, ask after you're done rolling (this doesn't apply to drilling). Never ask a higher belt to roll. If you're rolling and you start to get close to a higher belt then YOU must move and reset somewhere else. Always shake any black belts hands that are on the mats. Make sure you have footwear ON when you step OFF the mat. Be kind, courteous and thank everyone after rolling. You'll do great.
Oh yeah, welcome to Jiu-Jitsu