Multi-factor authentication (MFA) is a secure authentication method. It requires the user to prove their identity by supplying two or more pieces of evidence, the factors, when signing in. For example, a user logging in with their username and password is also required to supply a code sent to them by email or SMS or generated in an authentication app, approve the login attempt in an authentication app, or provide biometric data such as fingerprint or facial recognition scan.
The exact method depends on the authentication provider and how authentication and single sign-on, if you use it, has been set up in your org.
For more information on setting up multi-factor authentication in your org to meet the Salesforce requirements and managing users' associated authentication devices see the Sage People Community article and its links, or for more information about Salesforce multi-factor authentication in general, see the Salesforce help.
If a user needs to change device or leaves the organization, an administrator must disconnect their Salesforce Authenticator on the Users page. See the Salesforce help article: Disconnect Salesforce Authenticator from a User's Account.