Generally an event is only made available to a single group of people, however larger events (eg. a state-wide meeting, or disaster response) might involve several groups of people.
In this case, a single event can be shared amongst multiple groups of people, allowing managers from each group to roster staff and amend event details as required. This also allows information such as documents, action items, maps and so-forth to be distributed to everyone attending the event, regardless of the group they are part of. Expressions of interest can also be submitted by volunteers from each group in the same way they can for a normal event.
To share an event with other groups, you will need to first edit the event, then select the groups to share it with in the 'Sharing' tab.
Once saved, the event will automatically appear in the events list and event calendars.
Note that when an event is shared with other groups, this does not trigger the system to notify anyone whom it's been shared with - it's upto you as to whom you notify.