The Calendar view is accessible by clicking the link on the Toolbar at the top of every page.
The Calendar gives a visual representation of the Tasks you have permission to see. There is an option to show Sub-Tasks, apply and save varied filters, as well as toggle different Calendar views.
Tasks are shown as two items on the Calendar, one being each Task's Start Date and the other its Due Date. Clicking any of these will bring up a summary through which you can access the full Task Details, or you can also drag and drop either the Start or Due Date item to change the dates of the Task in question.