User groups can only be added by System Administrators or those users with additional permissions to Manage Users.
Go to the Settings on the top right of the menu.
Select Groups from the Settings menu. You will see all current Groups in the system.
Click the button New Group.
Here you will be asked to enter a name for the group. Enter the name and click Create. NB: Ensure you are not duplicating a group already in place, it may have a slightly different name.
Now you and other administrators can add users as needed to the group.