What is RSS?
RSS is a way of subscribing to a website. This means that you create a 'feed' from this website.
This feed informs you of changes to the site, such as new photos, people, families, history documents.
To use RSS you need to have a browser capable of reading RSS feeds, such as Mozilla Firefox or IE7 (not out yet, coming out Spring 2006).
For example in Firefox all you have to do is click on the orange icon as highlighted in the screen grab below:

You can also use online services like reader.google.com or www.newsgator.com
All this may sound complex but its actually pretty simple once you try it out.
RSS features of the beta IE7 browser are discussed at the MSDN blog.