To create a group in BuddyPress just follow some settings.
go to setting on dashboard >> select BuddyPress >> check both (Freind Connections and User groups ) and save the settings.
Another way is from the front end of the website. But before that make sure the Group is added to the menu
Now, see on the front of the website and you will find a menu of the Groups there where you can create new groups on a single click