you can use them to syndicate your own news column or information feed on other websites, or you can syndicate news / info from a site that offers a rss feed.
two things: one if you are using someones feed then you may be providing good content for your site.
then the person providing the feed usually will put a link on your page under the feed, providing him/her a link back on all those who are using the feed. (either that or they are charging a little $$ and you don’t have to put up with a link back)
did that make sense?