To subscribe to the calendar, so that you get all updates automatically, this link might work from your PC/MAC:
Subscribe to the calendar
But it seems more likely that you’ll have to cut-and-paste the calendar link. Here is the raw link:
The easiest way is to do this from a computer, not a phone. You go to your google calendars here: calendar.google.com. In the menus on the left, under "other calendars", you select the plus sign (+) and then, from the menu that appears, you select "by URL". That will pop up a box where you paste in the link from above and select "ADD Calendar".
Once you've added it, if you have an Android phone and you're using Google's calendar app, it ought to just appear in your calendar list. Same with using Google's calendar app on an iPhone.
But if you're using the Apple iphone calendar app, you have to do some extra magic. Follow this link and select the calendar there and then SAVE. That should make it appear. Usually.
Looks like you can also subscribe your iphone to the calendar directly from your phone.
For an iphone, these instructions seem to work:
You can also do the same to subscribe to the Holy Ascension Birthday and NamesDay calendar using this link: