How to setup multifactor authentication

I received this email (screenshot) saying that I must enable MFA by October 15. I get the impression that if I don't enable MFA, I will lose access to my Azure portal and resources. But I read the documentation links in the email and it is still very unclear to me what I need to do. I also browsed my Azure portal and I still can't figure it out.

I am the sole developer of an Azure-based web service I setup over ten years ago. Unfortunately, Azure has gotten very complex over the past decade and I am no longer "up to speed" on all its terminology and jargon. I just need "plain English" instructions so that I can continue to access my Azure portal and resources.