You can click on the link below to learn how to find your Google calendar address.
https://support.google.com/calendar/answer/37103
Then, please follow the steps below to add this calendar.
1. Log in to the portal of Office 365 through http://mail.gatech.edu with your account.
2. Click Calendar.
3. Right click on My Calendars and click open calendar.
4. Past the Google calendar address you just get into the box of Internet calendar and click open.