The sub-groups are mostly either special interest groups, like partners or freelancers. They could also be regional based, where the members meet up regionally.
Most of them are open for all members. Some only allow their members to participate, and again others are closed for non-members. New members may apply, but special requirements may exist for each group.
If you like to setup a new group, regional or within a special interests area, then contact the group management. Then we will help you get it started. Use the group contact form.