It is easy to enable the multi-factor authentication for a user. To enable, administrator permission is required. Once we enable the multi-factor authentication to the user then the user should pass through the authentication wherever that user wants to access.
For example, if you are Office 365 admin and you are enabling multi-factor authentication for a user. That user should go through the second authentication to login to email, power bi or whatever services that are connected with O365.
Follow the below steps to enable Multi-factor Authentication,