To use Two-Factor Authentication you will need to download the 'Google Authenticator' app to your mobile device (or another authenticator app of your choice such as the ‘Authy' app).
Once downloaded please go to; 'Settings' -> 'Two-Factor Authentication' and click ‘Enable Two-Factor Authentication’.
From here please scan the barcode from the authenticator app. This will add an entry into the authenticator app with a code next to it that updates every minute. Then click 'Enable Two-Factor Authentication' to continue.
After you have enabled Two-Factor Authentication you will have the option to copy your backup codes, please do this to avoid loosing access to your account should you misplace the device that you use for Two-Factor Authentication. After you've copied the codes please click 'Ok, got it. Take me to the exchange'.
On the next screen you will need to enter the code that you see in the authenticator app and click 'Enable Two-Factor Authentication'. (Please note your code will be different from the one in the screenshot).
We must reiterate that it is very important to save your backup codes in a secure place, otherwise you will be unable to access your account should you lose your phone. If you do lose your phone you have the risk of being locked out of your account, so please save your backup codes to avoid this risk.