Page groups allow you to call a phone and have it automatically answered and placed on speaker phone. This is useful for making announcements.
To add a page group, simply drag the page group tile across and drop it into the desired callflow.
This will then pop up with the page group creation screen as below:
You can then select which users, device or groups should be in the page group by dragging the option from the left hand box, into the main page group box.
Note that your phone must have a speaker function to be able to use page-group.