The first of line of verification is usually the password. After the correct password has been entered, a second step is initiated. This usually comes in the form of a passcode that can be sent to a filed phone number or email address. This ensures the person entering the password is the same one in control of the account.
In many cases the second, or even third level of authentication, takes the form of a biometric. This can include fingerprints or face ID scans, many now commonly used as part of security on mobile devices.