Hello! Just like on other platforms, the forums have ‘roles’ (called Groups here). These groups also let you see other members and the general activity of the group!
The Groups tab is in the “More” section of your sidebar.
There you’ll find groups you can immediately join! There may be some ‘closed’ groups which do require other means to obtain.
You can also go to your Profile→Preferences→Account→Flair to decide which group icon you want represented with your profile pic!