How does the Opigno Calendar Event Group Module work?

This module states that it "Provides a way to attach calendar events to groups". I expected something on the Add Event form or Edit Event form to add a group to an event, but I see no such ability. I gee the groups selectors to filter the available members on the form, but they don't appear to do anything beyond the filtering. Is there another place in the UI to add a group to an event?