If you want to add the calendar to your Google calendar, simply click on the button in the bottom right.
If you want to add the calendar to your own calendar app, simply copy the following URL and paste it into the relevant field (iCal URL): https://calendar.google.com/calendar/ical/dsd5oirtp5e6uhhh8e99j1i0vs%40group.calendar.google.com/public/basic.ics (Users of Windows Calendar need to add the calendar via their online Outlook calendar.)