Using it is very simple:
- if you haven't already got it, you'll need to download the app
- go to your settings and enable 2-Factor Authentication (2FA), and
- once it’s enabled, the service will ask you to take a snapshot of a QR code using the app
Android users: if you're using Google's Authenticator app and you haven't already got a QR code reader, you'll need one of these to get set up).