...
From the Administration bar, click on Dashboard.
Under the Vocabularies (right hand side), select Contact groups.
Select Add term.
Enter the name of the contact group in the Name field.
Click Save.
To re-arrange or nest Contact groups, click on the Dashboard again and select Contact groups under Vocabularies. Re-arrange the Contact groups by clicking on the arrows beside the name and dragging it to the desired location.
Click Save after re-arranging.