Click Add calendar. The calendar will appear in the Other calendars section of the calendar list to the left.
Note: It may take up to 8 hours for changes in ICS feeds to reflect in your Google Calendar.
If you have the iCalendar address of a calendar from a different application (for example, Apple's iCal), you can use this as well, it works for any ical feed. (directions from google https://goo.gl/Js4AMR )