In day and week views, a little icon showing three tux penguins is placed in the event, if you are the organizer of an groupscheduling event.
If you have an event-request in your inbox you can either press to ignore the request, or press , and insert it to your calendar. You should then edit your status in the event's attendee tab. And then send a reply by marking the event, and pressing ->. If you want to change the date/time of this event, change them, and then send back your proposal by pressing ->.