If MFA is 'Suggested ' or 'Mandatory' you will be taken to the Registration page.
Note: You will need to have already added an authentication App to your device - help here
To get to the registration page if the MFA is 'optional' then follow these steps...
1. Select your email address (top right) and then 'Profile'...
This will take you to your own user profile..
Select the 'Preferences' tab...
Setting up user MFA in GVO is in two parts - a one off registration authentication (using the Authentication App) and then periodic Login Authentication using the same App.
When you select 'Register for MFA' from the login screen or from preferences in your user profile you will be taken to the MFA registration page...
You need to scan the QR code into you Authentication App or type in the long code (suggest copy/paste). The Authenticator will generate a 6 digit code which you type into the boxes then press 'Complete Registration'. You will then be taken to your GVO account as normal and MFA registration is completed.
When you next login to GVO you will be asked to generate a login code - this will happen periodically based on the settings for Trusted Devices in your GVO (typically once every 30 days for each device you use).
Full Help about MFA here - MULTI-FACTOR AUTHENTICATION HELP