This article explains how to import ICS calendar files into Google Calendar and Apple Calendar. The article also contains information about the ICS format.
How to Import Ics into Google Calendar – Open your Ical file
Avoid schedule confusion by importing your information from all of your calendars into one application using an ICS file. After you export your calendar items as an ICS file with an .ics extension, you can import them into your favorite calendar. There, you can merge the items into your existing calendar or have the events appear in a new calendar within the application you're using.
Open Google Calendar at calendar.google.com.
Select the gear icon to the left of your profile picture at the top of Google Calendar.
