Synchronizing Google Calendar to Your Personal Calendar
Syncronizing with another Google Calendar
Click "+ Google Calendar" button/icon in the bottom-right corner of the calendar on this web page. Note: If you are having troubles seeing this calendar on your iPhone's calendar app,
Make sure you have added your Google Account to your calendar on your iPhone, via iPhone Settings > Accounts & Passwords
Check https://calendar.google.com/calendar/syncselect to make sure Shared Calendars are syncing.
Synchronizing with an iCal Calendar
Open your iCal calendar
Click File on the menu bar, and select "New Calendar Subscription"