You can see what domains are associated with your account.
It provides a view of all Users and to the Groups to which they are assigned as well as if a Group is setup to use a Tag. Tags are covered in another article.
If a User is assigned to more than one Group (assuming there isn't a Tag being used by any of the Groups) the User's signature will alternate equally between the Templates assigned to those Groups. Below you can see that Rebecca is assigned to three groups (Finance, Operations, Special Offer). When Rebecca sends her first email it will use the Template assigned to the Finance Group, her second email would use the Template assigned to the Operations Groups, her third would go back to using the Template assigned to the Finance Group, etc.
You can also see which User emails addresses are used within each of their Groups.