The easiest way to understand this is to try it.
In Firefox, go to any news site like
http://www.soccernet.com . On the far right side of the address bar there's a small orange icon that indicates that the site has an RSS feed. It looks a bit like this, only 100 times smaller:
Click on that icon, and save the live bookmark somewhere. When you go to check out that bookmark, you'll see that it automatically updates and creates temporary bookmarks containing headlines of the latest news stories. Click on one of those and you'll be taken to the full story.
I can't imagine how people can possibly read online news without RSS feeds.