Broadcasting to Room

You can start a Room Broadcast by going to More > Broadcast to Room.

You'll then be able to select people to participate in the broadcast. Whoever you select will be visible to the entire room.

If you start a Broadcast with 2 people, but then want to pull in Samantha, you can:

Hover over her initials at her table (to view her Virtual Business Card), then click Add to Broadcast or Remove from Broadcast.
Find her name in the Attendee dropdown, click the Options button, then click Add to Broadcast or Remove from Broadcast.