When you are logged into your account, tap on "Settings" then tap the box near "Enable 2FA via an Authenticator App".
Once you have an authentication app, you will be able to scan the QR code that is in front of you (Not the one in the image below).
Scan the QR code
Enter the "6-digit code" that you see on the authenticator app screen.
If you are having an issue scanning the QR code please click the “Unable to scan?” link and enter the code on the screen.