https://www.engadget.com/2006/04/13/howto-subscribe-to-a-google-calendar-using-ical/
Follow the instructions here and then be prepared to wait. For at least 15 minutes. Also, add the hotmail, gmail and icloud email addresses permitting them to make changes and view.
Don't freak out if it doesn't sync - give it some time and it will work out.
