explanation of this move?

en passant if it looked like this

Post 2 is correct. Your pawns had to be on f4, g7, and h6. Ages ago, pawns could only move 1 square, but it was decided to slightly speed up the game, by allowing on a pawns first move to move 2 squares. It was then noted that with the new rule a pawn by moving 2 squares could pass an opponent's pawn avoiding capture. To keep the game the same, en passant was made so when this took place, the pawn could be captured as if it had only moved 1 square. However, if one wishes to capture en passant it must be done immediately. you cannot move something else and then go back and capture later. When you moved from g7 to g5, you passed whites pawn on h5 with the 2 move rule. White captured (en passant) as if you had only move 1 square (g7 to g6) hxg6.