Please go to "Account" ➜ "Personal Information" ➜ "Security" and you will find "2 factor authentication". Turn in on.
Please install Google Authenticator on your mobile phone to enable the process of 2 factor authentication.
Open Google Authenticator and scan the barcode on the page, or copy and enter a 16-digit key.
Please insert the 6-digit verification code for Google Authenticator and press the open button.
Please note that: in the occasion that your phone is lost, you can recover your 2 factor authentication code with the 16-digit key. Please keep it in a secure place and refrain from disclosing it to others.