On your iPhone or iPad, open Settings
Tap Calendar
Tap Accounts
Tap Add Account
Tap Google
Sign in with your Google account
Turn on Calendars
Tap Save
On your Mac, open Calendar
Click Calendar in the menu bar
Click Add Account
Select Google
Sign in with your Google account
Enable Calendars
Click Done
To view the Google Calendar in Apple Calendar, open the Calendar app
Make sure the Google calendar is selected in the calendar list
If needed, refresh the app or wait for sync to complete