Hiya!
Welcome and very best of luck at group!
I personally love going to group and staying for Image Therapy. I feel it helps keep me on track and I love hearing other peoples' stories and seeing their progress. My group is really enjoyable and friendly bunch, so if I ever have any issues, they are right on hand to help.
At your first group, you will sit with the consultant and any other new members and he/she will explain SW and food optimising. I would advise you to stay for Image Therapy where you will sit with the group and the consultant will go through everyone's gains/losses, and see what help they can offer or if they have any concerns etc... Mine is very light hearted and engaging. Whilst it's an open group, it's very private and your weight is never disclosed. On your first meeting, you will just sit in and listen and be welcomed to the group - you won't be expected to say anything!
Let us know how it goes for you!