Two-Factor authentication allows you to have an additional layer of security to your account.
You have to have your phone number verified in order to use SMS 2FA, simply verify your phone number from the settings page.
To enable SMS 2FA simply click the second toggle on the "Settings" page. Then you will be asked to enter the one-time six-digit passcode that is sent to your phone.
When you get the code, enter it on the screen and click "Enable 2FA". If you did not get the code on your mobile phone, please click the "I didn't receive the code" button (You can resend the code once every 20 seconds).
Your account will now have 2FA enabled. Each time you log in you will be required to enter a one-time passcode sent to your phone.