A Chess engine is a program that will play chess. It is a program that will "think" and decide on chess moves to make. You can read about them here: http://en.wikipedia.org/wiki/Chess_engine . Please note, it is illegal to use engines during an ongoing chess.com game. The real advantage for them is to use after your game to maybe help you reaize where you went wrong, and how you might be able to play better.
As for CPT, I've not used it, so I can't really say. Hopefully someone else out there will be able to shed some light on that one for you. But I did manage to find a manual for it here: http://community.chesspositiontrainer.com/files/7/manual/entry8.aspx
I have looked at Arena to download. They say it needs an "engine."
And I downloaded Chess Position Trainer. And it would do nothing but say "New" and "Load." Following those out led me to "My documents" and I was supposed to save some file. I have no idea what all this about.
I want something I can download and it plays right away!
What does one do with CPT or Arena? What do we have to add to them to get them to play?
Confused...
stwils