HOW TO ACTIVATE TWO FACTOR AUTHENTICATION FACEBOOK

Two-factor authentication is a security feature that helps your Facebook account across the internet more secure from hackers .If you set up two-factor authentication, you'll be asked to enter a special login code  each time when tries accessing Facebook from a computer or mobile device we don't recognize. 

To turn on or manage two-factor authentication:

go to Settings.

tap Security and Login.
Scroll down to Use two-factor authentication. and click Edit Button.
Choose the authentication method you want to add.

Then, Follow the on-screen instruction.

Click Enable once you've selected and turned on an authentication method.