You can only add a calendar using a link if the other person's calendar is public.

1. On your computer, open Google Calendar.

2. On the left, above "My Calendars," click Add   From URL.

3. Enter the calendar's address in the field provided. The address needs to be the ICAL link below:
   https://calendar.google.com/calendar/ical/r8req31rh27iqdvfcv1mi0nago%40group.calendar.google.com/public/basic.ics

4. Click Add Calendar. The calendar will appear on the left side under "Other calendars."

Note: It might take up to 12 hours for changes to show in your Google Calendar.