Once you've set up a group appointment (date, start and end times, description, repeat interval), you may want to mail the group a reminder. With the group appointment displayed in the Group Appointment Editor:
Click More to display additional options.
Calendar displays a Compose window containing an appointment attachment. The appointment attachment is pre-addressed to the selected users and automatically filled out with the date and appointment start and end times.
Click Deliver in the Compose window.
Calendar mails the reminder to the selected users.
Recipients of a mail message with a calendar-formatted reminder can drag the message from the mailer header window and drop it on their calendars to automatically schedule the pre-formatted appointment.