Be sure to turn editing on in your Moodle course and find the 'Add a Block' drop down menu.
Once you select Calendar, your course will refresh and the Calendar block will appear on the left side of the course.
Due dates from assignments (and quiz dates) are automatically transferred to the Upcoming Events block.
Neither the Calendar nor the Upcoming Events block require any configuration other than selecting to load them from the "Blocks" block and dragging them to a desired location.
Posting events to the Calendar is easy. Just click on the "Go to calendar..." link at the bottom of the Upcoming Events block. You will see the following:
Click the New Event button and you will see:
Enter an Event title and a date, in neccessary, and click Save.
For more information about the Calendar and the Upcoming events block: