En Passant rule?

This is getting confusing :

En passant is a rule where you can take a pawn right next to yours if it has advanced two squares, like if it only had moved one square. However, you can only take en passant right after the pawn you want to take moves two squares.

What people are saying is that en passant can happen in "any stage in the game" ; what they mean by this is that it can happen in the opening, middlegame, endgame ... Any time in the game as long as the pawn you are going to capture moved two squares right on the move before ; after that, en passant is no longer possible, even if the pawns are correctly set up.

En passant is possible :

En passant is no longer possible after a4 :

If you are having trouble with this special rule visit :

https://www.chess.com/article/view/how-to-capture-en-passant