Recovery codes are one-time codes given to you when you turn on a second factor. Each works once, and they are shown only once, at the moment they are generated.
Save them somewhere that is not the device holding your authenticator app.
When you get them
When you turn on two-factor authentication with an authenticator app.
When you turn on SMS as the sign-in step. That gives you ten codes, shown once.
What they are for
They are the way back when every factor is lost: a phone that is gone, an authenticator app that was not backed up, a number that no longer receives messages. A recovery code answers the second step at sign-in, and it also answers it during a password reset.
They can also turn a second factor off: entering a recovery code, or a current authenticator code, is what disables two-factor authentication. A password alone does not.
They are not a password
A recovery code proves the second step, not the first. You still need your password, unless you are signing in with a passkey.
If you did not save them
There is no way to show them again. If you still have access to the account, turn the second factor off and on again to generate a new set, and save it this time.
If you cannot sign in at all, write to [email protected] with the account's e-mail address, which factors the account had, and the support code shown at the refusal. Nothing in the system lets support skip a second factor, so say clearly what you still have access to.
Quavern help reference: recovery-codes/en