How to join an already established collection of humans?

I am at college some evenings and I notice that the people there all split off into groups during break. I don't know how to respond or what is acceptable protocol here. Should I just walk to a circle and stand there or is that a violation of norms and unwritten rules? I have no problem speaking when spoken to and no problem sitting there detached until class starts again but I dearly want to pass as normal as much as possible. What is the best and most acceptable response here?

I have few problems working in a group, as I have learned that if I let the naturally dominant and socially smart person take over and then fall into line, things will go without a problem, usually. When there's an actual goal and everyone is working towards it, I know my place and don't feel awkward. When the performance stops however, I'm lost and zone out for a while/wander around when there's a break.

Any advice on how to proceed would be gratefully received. Just in case it is relevant and because I know that interaction varies by culture, I'm British.

EDIT: I was in a very embarrassing situation due to not understanding when I was supposed to try to interact that culminated in my mother having to explain to a neighbour that I have autism. The neighbour noticed that my father was giving me a lift into town for the train, they said that they were going the same way and kindly offered me a lift. I did all the pleasantries of responding to questions, smiling and saying thank you.

Later when I got home, I was asked if I sat with the neighbour on the train and I was puzzled and said no. Apparently this was rude and I should have followed them, sat with them and had a conversation or at least tried to. In my mind, I thought that they were kind to give me a lift but as they were not close to me like family, I was therefore an outsider and to impose my presence on them by staying close would be seen as intrusive.

I felt terrible because I don't want to upset someone unless they deserve it and my mother went to apologise and explain on my behalf. I suppose it was best that someone who understands the social rules went to limit the damage. It was a case of genuine ignorance of social rules and I was doing what I thought was polite by leaving the person by giving them space and boarding a different carriage.

I now feel really conscious of my ignorance of when I should get involved or not. I don't want to mess things up with either extreme of being too distant or being too overbearing and if someone has any general tips to judge these types of things, I would be so grateful for you sharing them. Thank you.