Calendar selection bar
The “Calendar selection bar” allows you to quickly turn single calendars on or off: You can turn it on under “Settings > Display and Use > General > Show calendar selection bar”. It will display a list of your calendars at the bottom of the screen and allows you to turn them on or off with a single tap:
Additionally you can long-press a calendar to show only events from that calendar. And by long-pressing it again, all other calendars are activated again.
If you don’t want to have all your visible calendars in the bar, you can specify which should be included under “Settings > Display and Use > General > Show calendar selection bar > Calendars”.