I was surprised to learn that you can download and use Shredder for free. I was also surprised to learn that a GUI is required and needs to be downloaded separately. I was happy to learn that you can find some decent-looking chessboard GUIs for free on the internet. My question is: once I download Shredder and the appropriate GUI, what do I need to do to get them to work together?
Out of topic, but if you want free chess engine with ready UI and very powerful engine, I would reccommend you to use Stockfish.
You have to use http://es.lichess.org/analysis It´s free and good.