Navigation
Heat Map
The Heat Map lives just to the left of the Timeline, and you can slide over to see it.
Changing Months
Swipe up and down on the Heat Map to change months. Tap the arrow 
to come back the current month.
Year View
You can tap the month name, or slide to the left to see all the months in the year
Switching Calendars
The Heat Map shows every event from your calendars. To quickly preview the events just for a particular calendar, press and hold on the Heatmap Preview button at the bottom of the screen then slide left and right to flick between calendars.