To start using Google SSO follow the directions bellow:
1) Start by opening your site settings from the Cog icon on the right side of the site header bar.
2) Click on "Authentication" in the left sidebar and turn the Google toggle on.
3) Click on "Configure Google Settings", enter your "Google Apps Domain" and click "Save".
4) You can also changed the name that appears on the on the login button by changing the "Login Button Text".
5) If you do not already have a "Google Apps Domain" you can get one by creating a Google Apps Business account at: http://www.google.com/a