RSS stands for "Really Simple Syndication." It is a way for you to get the latest content from this community, along with many other sites that you visit, all in one place. With an RSS feed reader, you subscribe to web sites, and those sites feed you new content so you can stay up to date.
To use RSS, you need a feed reader, such as Google Reader, MyYahoo, or the Live Bookmarks feature of Firefox. There are many free options. After you have your feed reader set up, you can find RSS feeds in the community by going to a board, blog, thread, or message and selecting Subscribe to RSS Feed from the options menu. There you will see a preview of the feed. Most RSS readers give you a button to click at this point. After you click it, the RSS feed appears in your reader as well as new content from that section of the community whenever it becomes available