Once you have logged into the website visit your Profile center by clicking on your username at the top of the screen and select Profile in the dropdown. From there click on the last icon in the profile navigation bar named Profile.

Click on the Two Factor authentication button and check the enable two factor authentication checkbox. Scan the QR code (removed for security reasons) with your phone. Once you have scanned the QR code successfully with either app you can click change and it will be activated.

Download Apps

Click the link to the store which is most appropriate for your type of phone.