2 factor authentication is where you will give a company your mobile phone number so that they can issue you with a code that you enter to access their service on your computer , tablet or smartphone.
Passwords are great , but 2 factor authentication means that they know it is you.
So where are some of the sites and services that you can turn it on:
Activate it , turn it on and use it
More information can be found at this CNET Article