RSS (Rich Site Summary) is a format for delivering regularly changing web content. Many news-related sites, weblogs and other online publishers syndicate their content as an RSS Feed to whoever wants it.
RSS solves a problem for people who regularly use the web. It allows you to easily stay informed by retrieving the latest content from the sites you are interested in. You save time by not needing to visit each site individually. You ensure your privacy, by not needing to join each site's email newsletter. The number of sites offering RSS feeds is growing rapidly and includes big names like Yahoo News.
Feed Reader or News Aggregator software allow you to grab the RSS feeds from various sites and display them for you to read and use.
A variety of RSS Readers are available for different platforms. Some popular feed readers include Amphetadesk (Windows, Linux, Mac), FeedReader (Windows), and NewsGator (Windows - integrates with Outlook). There are also a number of web-based feed readers available. My Yahoo, Bloglines, and Google Reader are popular web-based feed readers.
Once you have your Feed Reader, it is a matter of finding sites that syndicate content and adding their RSS feed to the list of feeds your Feed Reader checks. Many sites display a small icon with the acronyms RSS, XML, or RDF to let you know a feed is available.