What is it like to be in a writing group?

I am curious as to what it is like to be in a writing group. I have been invited into one and while I am giving it a shot, I can’t seem to grasp what it really means to be in one. I have seen many different ways of writing groups, some are online and some are in person. I have seen some writing groups written about in books and I have seen one in a movie. Some seem to be overly critical and only see the flaws of what is written, while some only see the good. I am only 15 so the writing group I am in is made up of my friends. What am I supposed to do to be a good member of the group? Do I only offer criticism, or do I offer positive feedback every once in a while?<br>Thanks to everybody who replied to my previous post. I appreciate all the useful advice. I am excited to see where this takes me.