You can only take by en passant right after the pawn you’d be capturing moved. If you do not take en passant on the subsequent move you have forfeited the ability to take en passant. Likewise, if you ended up in the same position in any way other than your opponent moving their pawn up two spaces you cannot take by en passant. [3] X Research source Your opponent must have moved their pawn two squares forward. If the position was reached in another way you cannot play en passant. [4] X Research source Both pawns must be on the fifth rank (if you’re playing white) or the fourth rank (if you’re playing black). Only pawns can be taken by en passant. Only pawns can play en passant. If any of these do not apply to you (or your opponent) you cannot play en passant.
Write the file the pawn started on in lowercase. Write an “x” to signify the move was a capture. Write the square the pawn is now on. (e. g. exf3)
Try looking online for visuals. Some players find it easier to understand this way.
