The game has a built-in tutorial so that you can learn the basics. Maybe it would be best to start off by playing regular Sins, then by moving on to Entrenchment, and then Diplomacy. Once you understand regular Sins it isn't too hard to pick up the expansions one by one.
He said he wants a trainer, he didn't say anything about having trouble beating the game or needing help learning how to play. Personally, I've never used a trainer for that reason (not that I've bothered with one at all for at least 8 years), but rather just as a means of having some fun outside of the natural conditions of the game.
