About RSS [Feeds]
Related links
Firefox
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Internet Explorer
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What is RSS?
In general, RSS is used as the abbreviated version of 'Really Simple Syndication' (however, there are different standards so it might also be used elsewhere, for example, to refer to 'Rich Site Summary').
Basically, RSS allows you to see when website's have added new content. You can get the latest updates in one place [see below - managing feeds], as they are published, without having to go directly to the websites you have taken the feed from.
Note: you might also come across Atom feeds, these are similar but use a different schema.
Finding feeds
RSS feeds are increasingly common on websites; while they might simply be presented as
a plain link, they are more commonly 'advertised' with a descriptive link and a specific icon -
the following icon is often used. 
Managing feeds
The first thing you generally need is a feed reader/news aggregator. There are numerous readers/aggregators about and various ways to access the feeds e.g. via modern web browsers, downloadable applications, web based readers, ‘mobile’ readers, etc.
Browsers: if you are using IE7+, Firefox, Safari, Opera or Flock, for example, you can subscribe to a feed via the browser; simply use the relevant link(s) provided by the website to view the feeds and decide where to subscribe them to.
Note: RSS feeds won't be read properly in older browsers, e.g. IE6 (they will be rendered as source code) - choose one of the options below.
Web based: amongst others - you can manage feeds via, Google Reader/iGoogle, My Yahoo, Bloglines, NewsGator and Pageflakes.
Mobile: most of the methods mentioned here have also been adapted for modern mobile devices.
Desktop Applications: FeedDemon [news aggregator], for instance, is a popular Windows based application which is provided by and integrates with NewsGator; they also offer NetNewsWire for Mac OS X.
Note: you can even add feeds to Outlook …