Subscribers in the local address book can be combined in "Groups". Groups simplify conference management adding whole subscribers groups in the conference in one click. To create new subscriber group go to "Home"->"Address book" window and and click on "New group" reference, as per picture below.
Create new group
To move subscriber to another group just click on the subscriber and click on "Move to group", see picture below. Subscriber can share several groups.
Groups of subscribers
Address book can be considered as a two level hierarchical tree where ungrouped subscribers lie on the first level and grouped subscribers on the second level.