1.6. How to sync iPhone and iPad Calendars via iCloud

In case you've selected Local Calendar at first start you can sync Calendars 5 on your iPad and iPhone via iCloud

1. Go the iOS Settings on your device  .        
2. Tap "Apple Banner" at the very top, go to iCloud. If you're using iOS 10.3.3 or earlier, go to device Settings > iCloud.
3. Once connected to your iCloud account, turn on the Calendars toggle.

If you use iCal on your Mac as well, you may easily enable iCloud calendars syncing.    

Note: this kind of syncing works with iCal only. Thus, when Calendars 5 syncs with Google account, events from Google cannot be pushed to Mac via iCloud.