The Calendar block can be found on the right hand column of most courses, although instructors are free to move that if they wish. 

If you go to the full Calendar (see link above), Moodle provides users with an integrated calendar that can hold 4 different types of events.

Global (event viewable in all courses - created by admin users) 
Course (event viewable only to course members - created by teachers) 
Group (event viewable only by members of a group - created by teachers) 
User (personal event a student user can create - viewable only by the user)

The calendar is integrated with many of the activity modules and can help you and your students stay organized. For example any assignment or quiz that has a closing date applied to it automatically shows up as a course event within student calendars. The individual events become hyperlinks when marked in the calendar, and students can navigate to the activities via the calendar block.

Some of the benefits of having an integrated calendar:

• Course activity related events do not need to manually be populated.
• Easy way to navigate the course according to the most urgent needs.
• Great way to remind students of upcoming due dates.