What is 'All Calendars'? How do I use it?

About All Calendars

・View multiple calendars at the same time

・View TimeTree calendars with other calendars ( Google Calendar, iCloud, and more)

How do I use it?

・Tap on the upper left corner

・Tap "All Calendars"

・Tap settings on the lower right corner

・Select calendar(s) to display

The "All Calendars" view is not available while using the web version.