When setting up TFA it is suggested that you also print your backup codes. Store these in a secure location like a safe or a locked filing cabinet. You can use these codes to get into your account if you lose access to all of your TFA devices.

Backup codes will only show up once you have enabled TFA.

Codes are single-use only. If you use a backup code then it will be deleted and a new one will be generated. If using a backup code, be sure to go into the TFA settings area and update your settings to avoid being locked out again.