In order to activate Google Two-Factor Authentication, you have to open your "Security" settings, which can be found in the dropdown menu when you hover the mouse over your profile’s icon in the top right corner of the main toolbar.
In the ‘Security’ section, please find the paragraph ‘Two-factor authentication system’ and click on the button ‘Enable’.
The system will generate a unique 2FA QR code that should be scanned with your Google Authenticator application which can be downloaded from App Store and Google Play. Once you scanned the QR code, the application will provide you with your authentication code that you should enter into the field "2FA Code". After you entered the code, simply click on the button "Done".
Please note, that system generates a QR code along with a secret account token, which can be
used in future to recover access to your account if you lost your phone with an installed Google
2FA app. Consider saving it in a safe place.