2FA is two factor authentication.
The first factor is your user+password. This is good, when you got a good password. But if your computer got infected by a trojan all your passwords will seen by the hackers too. So they can use all your accounts.
Here comes the second factor. The second factor is usually a pc independent code, you have to enter after you entered your password.
This can be an SMS, or a mobile phone app. The mostly used app is Google Authenticator: https://play.google.com/store/apps/details?id=com.google.android.apps.authenticator2&hl=en
To use this method (Google App) you must install it to your phone (or tablet).
Then you go to the webpage, and turn on 2FA. Usually you'll see a barcode. Just scan it with your phone in the Google app, and it'll write your current code. The code changed from time to time.
Remember, to save the barcode for later if you lost your phone or it breaks.
But remember to save the barcode on an external drive, so hackers won't get it, and can't use it.
Also important to use all the security stuff the webpages gives to you, to help you recover your lost password.
Once a hacker gets your account you should be able to get it back by the 'forgotten password' feature. (for example the site will send you an sms with a code to identify yourself as the original owner of the account).
Thank you for reading and safe browsing!
