I believe its just a way to find others with a similar interest or belief. Near as i can tell they are not heavily used. Most people join, then forget they're in them. Though there may be some that are more active.
To create one look at the top you'll see 'Quick Links' on the right side. Click that, then click 'Chat Groups' from the drop down menu. The bottom of the page has a link to create a new group.