how do I sync my calendar

If you're having issues syncing, see if this helps: If your iCloud Contacts, Calendars, or Reminders won’t sync - Apple Support

Your calendar can be selected as an option when you add an internet account with which to sync. Settings > Calendar > Accounts. You can also review general calendar settings at Settings > Calendar

The calendar does not sync between devices. they sync with the email client server which hosts your calendar.

Where is the calendar events stored on your iPhone? Please add the email account, that's it.

See the iPhone and Mac Calendar Pics below

When you add events to the Calendar it gets added to the Default Calendar set on your device.

See the pic below