RSS is one of useful features which many net user are not aware of. Simply put it is an easy way to get updated about new contents from the sites with actually visiting each site. Technically a RSS or news feed is just a text file in XML format (don't worry, you need not know what it is), which is regularly updated by a website with information regarding new contents in that site. This text file in XML format is not easy to read format but it is a format which RSS readers or aggregators can read and display in an friendly way. So by reading news feeds of a site using an RSS reader you can easily know about new content in a site.
The sites publishing RSS feeds will have some indicators like , or to inform visitors about presence of RSS feeds. On clicking these icon you get the URL of the RSS feed, which you can post in RSS readers. Newer browsers also detect the feed and show it in the address bar.
There are different types of RSS readers. Some require that you are connected to Internet for reading the feeds(online RSS readers) and some allow you to download all the new feeds and lets you browse through them even if you are offline(offline RSS readers).
There are lot of RSS reader both free and commercial, few RSS readers are given
Online RSS readers
Google reader : online RSS reader from Google (now discontinued)