Backup Codes could be used in case of emergency access if you get locked out. Each of the listed codes can be used only once, you can use them in case of emergency, when none of the other Two Factor Authentication methods you've set up can be used. For example, if your phone is out of battery or misplaced.
For this please go in menu "My Account -> Two-Factor Auth" and then click on "Print these codes" in the "Backup Codes" section.
A new window will be prompted, just print/copy these listed codes in a secure place.
We recommend you to generate a new set of backup codes regularly to avoid any abuse or if you think your backup codes are compromised, e.g. someone got hold of a printout with them, or if you are running low on available backup codes.