How to add a Google calendar shared with me, to my iCloud calendars
There are two methods:

Method 1:


When you open the link of the calendar shared with you. You could click the plus sign at the right corner to add it into your own google calendar.

Go to https://www.google.com/calendar/syncselect and check the calendar shared with you.
Go to the Mac Calendar and you will find it in your calendar list just under your google account. Check it for display.


Method 2:


As step 1 in Method 1.
Go to the Google Calendar and the shared calendar appears in the "Other calendars", go to the setting of the shared calendar.
Scroll down and find the "Integrate calendar->public address in iCal format" and copy the address.
Open the Mac Calendar and go to "Files -> New Calendar Subscription" and paste the address into the "Calendar URL".


Hope this would work.