To add an item to the calendar you must be logged on so first enter you username and password then click on the 'Add an event' link at the bottom of the calendar.
From there you will be presented with a calendar event entry dialog including six tabs. We'll only go over the first two tabs here since that is the essential part of getting something properly published.
Follow the steps in the image above then click on the next tab 'Calendar' to set up the date/time and whether the event is recurring.
Just use the date picker buttons to select the date then set a time for your event. If the event is recurring go ahead and set up the recurrence then click on the 'save' button and you're done.