RSS stands for Really Simple Syndication or it's sometimes referred to as Rich Site Summary. It's an XML-based content format for distributing news, headlines, content, etc.
Most popular sites, news sites and blogs provide RSS feeds for you to subscribe to. All you need is a feed reader to view its contents. Feed readers come in all shapes and sizes these days. The Firefox browser has one built right into the Bookmarks feature.
You can also create feeds for your own website so your audience can subscribe to them.