What are Smart Meters and Electromagnetic Fields?

After spending more than my allotted screen time on this site and this site, I've learned that I don't know much about Smart Meters and Electromagnetic Fields.  In fact, I felt rather silly reading about this and feeling like I was in the ignorant camp on this issue.

Oops!  I am very sensitive to foods, smells, and weather.  So I can't imagine what people go through who are sensitive to EM and it's effects.  Yikes it sounds awful.  Hopefully I nor my family have these issues and we don't even know it.

Do you know some things about this issue?  I want to know more.