To accept or decline an invitation to an event from the Calendar section:
1.Open the window with information about the event.
2.Click the appropriate button: Accept, Tentative, Reject.
3.For a recurring event, select the appropriate option in the response menu that opens: respond to one (selected) event or to the entire series of recurring events.
The event will be marked in your calendar according to your response to the invitation.
The responses of all participants in the event are displayed in the event information in the window to the left of the participant's name.
An invitation to an event can also be accepted or declined in an email sent to the invited participant's email.