In a nutshell, 2 factor authentication means you need something else besides a name & password to log into an account. Microsoft uses a cut down version of this when from time to time you have to verify a Microsoft account, e.g. entering a code you had sent to you in an email, same as when a company with a GOTD offer sends you a link via email to verify your email address.

Two factor authentication is not a cure-all -- it can be beaten -- but it can help quite a bit, since beating it does take extra time, effort, & skill. When you enable & use it, if someone(s) has your login info, e.g. from a phishing scam or web site compromise, it won't do them any good, because only you have that 2nd piece to the puzzle. This article has more...

androidcentral[.]com/two-factor-authentication-what-you-need-know

"Two-factor authentication: What you need to know"