RSS feeds are based on tags.
To create a RSS feed, go the Tags
Here, you will have to decide if you want a tag you've already made to have a RSS feed for it. Say you want all the articles that are featured to have a feed - open the tag "featured." Or, you can create a new tag that you can apply to the articles that you want in the feed. To do this, simply click "new" instead.
Once in the tag editor, you will see a section called "Edit Feed for this Tag." In this area, you can enable the RSS feed for this tag. You can give it a new title (say, if you're tag is "featured" but you want the RSS viewer to see "Featured Articles") and put in the author name, if you wish. Then pick how many articles you want in the feed. Finally, check the box that says "Enabled?" in order for your RSS feed to be activated.