Two-factor authentication is where when you log on a computer or in a site on the computer you not only enter a password or PIN number and also one additional piece of information. Usually it is the first item entered is something you know but could be something of you.
Something you know would be things like passwords and PINs that are easily stolen or faked. Something of you could be where the computer scans your finger print or does an iris scan, which are unique things about you.
The second item is usually something you were given temporarily, quite often where the place you are logging in sends a code to a device, such as your cell phone, and you must enter that code. Cuts down the chances of someone hacking in as you as they must have that device also. However, it does mean for you to log in you must have that device.
To set up two facto authentication in Facebook you will go to your account settings. Here is the process. First be logged in Facebook. Go to the drop-down arrow on the right side of the search bar line, it is a triangle pointing down, and click on it. Click Settings. Click Security and Login. To this point is how you can also change your password which you could choose here.
However, we are not changing password so click Click the edit button on the right on the line that has Use two-factor authentication. Click button with Get Started. You can choose to use an app, but I am showing where you get a text message, so select Get a text message select button in Text message box. Make sure it is showing your cell number (if not click change number and follow those directions) and click Next. Now you will enter the code sent to your phone. It may take a moment before the code arrives, if not arrive soon, click Resend code. It may have you click next or in my case it skipped that when I typed in code. Click Finish and you are now using two-factor authentication.
If you did this and do not want two-factor authentication, the next time you login Facebook you will get a screen you can turn it off, or after that time you can go back to the same place in Settings, we turned it on and you can turn it off there.