I’m looking for a site with a nice clear explanation of what RSS is, why it’s a good thing, and how RSS files work.

I’m looking for a site with a nice clear explanation of what RSS is, why it’s a good thing, and how RSS files work. If I can find such a site, I can use it to help me convince web sites to add support–or so I hope. I could write a simple “why I want it” sort of explanation myself, but I don’t have the knowledge to explain the “how.”