XML is a simple way of storing data. RSS is a standard XML format used for distributing news or anything as long as each item of data is classified in the same way. Beware of the slightly different RSS standards though, which is why sites like feedburner are great for converting them to work with all the different format readers. The RSS files themselves are just content with no design etc. People can view them with any software they want or even embed them in their own websites etc. So if you want to create content for others to see then RSS is a really easy way to distribute it.