En passant is French for "in passing". The term refers to a special move in chess where a pawn is 3 squares away from promoting (5th rank for white and 4th rank for black), and an opponent's pawn of an adjacent file moves to the same rank as your pawn. The tutorial dialogues go into a deeper explanation of this move. If you play enough chess, you will get this achievement naturally, though it may not occur for tens of games. Luckily, there is an easy alternative method. The following video will show you how to get this achievement along with two others:
-From the main menu, go to "Tutorials"
-Go to "En Passant Capture" (Page 7)
-Complete the tutorial by moving the pawn on e5 to f6 (you will need to press
to get through some tutorial boxes first)