An RSS (Really Simple Syndication) Reader is a web feed aggregator, also known as a feed reader, that aggregates syndicated web content such as news headlines, blogs, podcasts, and vlogs in a single location for easy viewing.
Examples of popular RSS Readers include Google Reader, Netvibes, Bloglines and My Yahoo's RSS feature. Once you have decided which Reader you are going to use, you sign up for an account and then look for RSS Reader buttons on your favorite sites and blogs (they are usually orange). You click on those buttons to add content to RSS Reader. It will update throughout the day, giving you the latest content from your favorite sites.
Why are RSS Readers great? They reduce the time and effort you'll have to extend checking your favorite websites for updates. Once you are subscribed to a feed, an aggregator is able to check for new content at user-determined intervals and retrieve the update. Also you can easily unsubscribe from a feed if you get tired of a site.
Still confused? Check out RSS Explained the Oprah Way for more help.