If you want to enable Google Authenticator (GA), please follow the below steps:
1) Install the Google Authenticator app on your mobile device
2) Scan the QR code on the Profile page with the App
3) Enter the six-digit code that appears on the App
4) Press "Enable" to activate GA
If you failed on the third step when it says "GA code is invalid", please go over again from the first step.
For more detailed instructions, please log in to your account, and refer to the Google Authenticator session on the Profile page.