I really suggest that you take the MSF class. I took it and it did wonders for me. It helped me feel more confident on the bike and not sorry jumpy. On the other hand, it would not hurt that much if you just rode in parking lots and what not... You are not going to become an expert right after the class. Just like everything else in life, experience is where you actually learn. The more you ride, the more you become better. So the decision is really up to you, just depends how comfortable you feel on a bike at this moment. If you are a little weary, then wait for the class, but if you feel pretty good, then just tool around and enjoy, but make sure you limit it to that. If that is your decision, make sure your friend helps you with the basics, starting, stopping, cornering, evasive manuevers.