When you log in for the first time, there is an extra verification step. You will need to use your mobile phone where you install Microsoft Authenticator or Google Authenticator.
In PlatformManager, you are prompted to scan a QR code and then the authenticator app will provide the verification code.
The verification code is required only when a user logs in for the first time from a new environment. An environment is defined as: IP address + browser + browser version + computer. Five environments are stored for each user. If the user does not have an environment saved, the verification code is requested. This new environment is then saved and replaces the oldest one.