Free readers are available as well; a search for "Feed reader" or "Feed aggregator" at popular search sites will yield many results.
If you have a website, blog, audio/video content, or even photos, you can offer a feed of your content as an option.
If you are using a popular blogging platform or publishing tool like Type Pad, Wordpress, or Blogger, you likely publish a feed automatically.
RSS feeds can be viewed as plain text files, but they're really designed for computer-to-computer communication.
We should point out that RSS is just one standard for expressing feeds as XML. Both formats have their boosters, and it doesn't appear that consolidation toward a single standard is imminent.