They are used to aggregate information. For instance, its baked into wordpress so make a post and go here http://pingomatic.com/ to send said post up the pipe. See wiki for a bit of history http://en.wikipedia.org/wiki/RSS hope that helps, Nigel
RSS feeds is a great way for your blog readers to read your posts. They add your feed url in a google reader ant get every post you write. But if a reader subscribed to your RSS feed you will not get an unique visitor, because reader will read all post on reader, but with feedburner you can add adsense to your feeds. Good luck!
Ok, i don't mean to be rude here but such open and wide topics can easily be searched on and you can find yourself loads of information through that. The second link posted by Nigel in the first reply to this thread is quite informative on that topic. Worth a read.