Emacs provides all the usual functions of a calendar, with a diary of past or planned events. To see a three-month calendar centered around the current month, use the command M-x calendar. Emacs will display a window with the calendar, point will indicate the current date, and you will be in Calendar mode.
You can move through the calendar from the current date to other dates. If you move outside the three months originally displayed, the calendar display scrolls automatically through time.