RSS in Plain English does a great job at explaining RSS in a simple, visual manner. The whole thing is done on a whiteboard, with a voiceover and pre-made bits of paper.
The video has everything someone needs to know to understand RSS, and get started using it. CommonCraft.com (the maker of the video) recommends Google Reader, and provides instructions on creating an account and adding feeds, though the video also shows URLs for alternatives.
It’s a great video, and I think Lee LeFever really found the best metaphor to describe RSS: It’s like Netflix, for the web. Instead of going and looking for content (e.g. going to Blockbuster) the content comes to you.