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 'Add calendar'.
3. Select 'Subscribe from web'.
4. Paste the Google Calendar address and click 'Import'.