Sharing calendars is part of Family and Business.
- In Calendar, find the calendar in the sidebar and choose Share calendar.
- Choose who to share with and whether they may only see it or also edit it.
Calendars shared with you appear under Shared calendars. The calendar stays encrypted; the people you share with get their own key to it.
To send a single event to someone, open it and choose Share. They receive it as an .ics file they can add to any calendar.