At PPL (as superally has mentioned that he is sitting), if you fail an exam, then the examiner is not allowed to go through the questions that you got wrong; they only do that when you pass!
Air Law does not really have "concepts" so understanding is really not so much part of the game. Light signals? You don't "understand" them, you learn them! Same for quadrantal rule, same for visibility minima und so weiter!
Cheers
Whirls