RSS is important for those who use to read some things like blog or articles so what the usual do they click on RSS button and they subscribe on that blog so every time the admin of blog update his blog with some new information , so if you subscribe you that information blog you dont need to go direct to that blog , the obly thing you need to do is that you to open your google reader if you have sign for that so you can see that at your left hand side you will see some small tabs or topic for which you had subscribed Thanks bye if you need any more information you can search on Google and you can find a video in plain English
Do not think that RSS feed is enough for subscribers.. As like you asked what is it as many visitors of your blog may not know what is it too. So the better idea here is to have both e-mail subscription and rss subscription to cover more visitors needs.
Googled it for better result... think will help What is RSS? RSS (Rich Site Summary) is a format for delivering regularly changing web content. Many news-related sites, weblogs and other online publishers syndicate their content as an RSS Feed to whoever wants it. Why RSS? Benefits and Reasons for using RSS RSS solves a problem for people who regularly use the web. It allows you to easily stay informed by retrieving the latest content from the sites you are interested in. You save time by not needing to visit each site individually. You ensure your privacy, by not needing to join each site's email newsletter. The number of sites offering RSS feeds is growing rapidly and includes big names like Yahoo News. What do I need to do to read an RSS Feed? RSS Feed Readers and News Aggregators Feed Reader or News Aggregator software allow you to grab the RSS feeds from various sites and display them for you to read and use. A variety of RSS Readers are available for different platforms. Some popular feed readers include Amphetadesk (Windows, Linux, Mac), FeedReader (Windows), and NewsGator (Windows - integrates with Outlook). There are also a number of web-based feed readers available. My Yahoo, Bloglines, and Google Reader are popular web-based feed readers. Once you have your Feed Reader, it is a matter of finding sites that syndicate content and adding their RSS feed to the list of feeds your Feed Reader checks. Many sites display a small icon with the acronyms RSS, XML, or RDF to let you know a feed is available. WhatIsRSS.com now has a blog ... We have always wanted to keep this resource brief and to the point, but we realise there is alot more that can be communicated about using RSS. Our RSS Blog was launched 26 July 2007 to extend and complement the information provided here. If you are interested in learning more about RSS go there now and subscribe! It will be updated over time with information on using RSS and will feature tools to help you use RSS in new and better ways.
Everything is pretty much covered above but the best place to answer your question is "www.whatisrss.com" cheers!