The calendar displays entries regarding the course calendar as well as the calendar of your learning group.
The link Search events enables you to search for events in order to delete them if necessary.
Additionally you can subscribe to any course calendar you want in order to let its entries appear in your personal calendar, too.
In order to create a calendar entry just click on the calendar sheet or use the calendar icon within the calendar list. In order to edit an entry already existing just click on that entry's date.