There a few different ways to launch a Group FaceTime call. One way is through the FaceTime app itself, where you can add contacts, phone numbers, and emails to a group.
You can also launch a group call through any of your existing group conversation in Messages. Tapping the contacts at the top of a group chat will reveal the FaceTime icon to start you call.
There are a couple ways to enter a Group FaceTime call that someone else started. This also means you can join into a video call at any time while it's going on.
From the Lock Screen or Notification Center, just tap the notification to be automatically connected.
Through the Messages app, tap the notification that appears at the top of your screen, or tap "Join" in the group conversation to enter the Group FaceTime call.
