The Account Owner or a Super Admin can create User Groups from the Users panel.
Once a Group is created under the Users panel, by the Account Owner or a Super Admin, Users can be assigned to this Group. Users can be moved to other Groups at any point.
The Group Admin can create new Users as well, but only within the Group they are assigned to.
If sharing is restricted at account level (globally) by the Account Owner, then only the super Admin or Group Admin can give access to a form or Folder outside of a Group.