The Calendar page contains your account's publishing calendar. You can access it through the account level menu.
The calendar will only display items that have at least one workflow status with a due date. Items are color-coded to indicate their expected workflow status for that date.
By default, the calendar is in month view, but you can change it to week view if you want using the view switcher in the upper right corner of the calendar.
Clicking an item in the calendar brings out more information about it such as its expected workflow status for that date, who's responsible, etc. You can click the item name to view or edit its content and you can also change its due date by clicking "manage deadlines".
Clicking on manage deadlines will bring up a modal that will let you change not only due dates but responsible users as well, as shown below.
Tip: If you want to assign someone to a workflow status but their name doesn't appear on the list, check out why can't I assign a user to a task.