so, hello and welcome to the forums
surely ultrafractal is commercial, but its free-mode is one of the kindest i know, because the only thing you have to pay for is the export for big images, so learning stuff and experimenting is really the best choice to get a grasp on what is going on ...
you might take a look at news #4 from this channel to get an idea
, not really an introduction, more or less an overview about current techniques, but its from me, and i need to promote:
http://www.youtube.com/user/kommissario?feature=mhee