Newbie question about RSS

I'm on a learning curve here, so can someone tell me if I have this right?
An RSS feed can be 3 different things.
1) An eCommerce site could use it to pass info on all their products to their affiliates, so the affiliates could sell them.
2) An article website could use them to pass on all the articles from their author(s).
3) A newspaper/magazine could use them to pass on their daily/weekly/monthly articles.
So a RSS feed would collect all the database, and deliver it to whoever requested it.
Then you would have just a database of items/articles. So to organize/access the data, you would need a Content Management System or CMS (unless you built your own database item by item).
So ...
That would leave you with the database on your hd, where you could use it to write articles, or pick items to put on your website. But if you wanted to put the RSS feed on your website, you would need a website that was designed to do that, right? A CMS doesn't publish the RSS feed to the web, it just organizes it? Although sometimes people package the RSS, CMS and website together.
And ...
if you get a RSS feed today, and wanted it updated next week, would you have to download the whole thing again, or can it just pick updated info? And can you filter the request to pick up just certain articles?

 

Well an RSS feed can be used for anything not just the scenarios you mentioned! Anything that needs to be delivered to users and get updated from time to time can use RSS feeds.
And no you don't have to have a site that is desined to have an RSS feed, you can implement an RSS feed to any site you want (providing you know what you want to provide in the feed). It is actualy very simple to implement an RSS feed.