The current specification is RSS 2.0 available at the Berkman Center for Internet & Society at Harvard Law School.
Places you'll see RSS:
Many tech websites: java.net, xml.com, etc.
News websites: CNN.com, sfgate.com, etc.
Many techies have their own RSS feeds.
RSS is easy. It is just an XML document on you website! ...but you can make it more complicated if you wish.