Set up multifactor authentication for users – Microsoft 365 admin

Multifactor authentication means you and your employees must provide more than one way to sign in to Microsoft 365. Security defaults offer a good level of additional sign-in security. If you purchased your subscription or trial after October 21, 2019, security defaults have been automatically enabled for your subscription. Conditional Access policies can offer you more control of your organization’s security needs, such as Microsoft 365 E5 and Microsoft 365 Premium P1 licenses. For more information about the Azure AD P1 license, see Microsoft 365 P1 and P2.”]

Source: https://docs.microsoft.com/en-us/microsoft-365/admin/security-and-compliance/set-up-multi-factor-authentication?view=o365-worldwide