Hi Angelwings.
Support groups don't always follow a standard format. What I would suggest is to use your first time as a way to learn how the group works. Someone will probably be a leader or facilitator. They usually explain how the group works, what the confidentiality rules are, etc. The ones I've been to have been pretty laid back, but it has been a while since I've gone to a meeting.

I used to co-facilitate an affective d/o support group. We made sure everyone had a chance to speak up. We also made sure that if someone wasn't up to participating they knew they were free to sit there and listen. We never needled anyone who didn't want to participate.

I hope you have a great time and that this experience is as helpful to you as it was to me.