RSS stands for Really Simple Syndication and allows you to subscribe to sites that have RSS feeds. After subscribing to a feed your RSS reader will check for new content from your subscriptions on a regular basis, download it and allow you to read these new items.
Once you download a reader click on the RSS icon – found for both posts and comments. If you click the icon for posts your reader will track new posts found on the site, same with the comments. If you choose both, your reader will search for both posts and comments.
Many blogs, websites and news services today allow for subscriptions and your one reader will work for all of them, so look around and have fun.