Here’s a useful site with lots of technical information, with many articles written by Jon Paris and/or Susan Gantner, two great educational resources.
Here are two articles which give some specifics on RPG /Free. There are others which build upon these, as new features have been introduced over the years.
<a href=”http://www.ibmsystemsmag.com/i5/september02/enewsletterexclusive/8181p1.aspx”>iSeries EXTRA — Free Ride: A look at free-form calc support</a>
<a href=”http://www.ibmsystemsmag.com/i5/may01/features/7235p1.aspx”>New Language? No, it’s RPG IV</a>