En passant is lesson 2 of 2 in Castling and en passant drills, a basics course suited to players rated around 400 (complete beginners). En passant is a pawn capture that only happens at one moment. Miss that moment, and the chance is gone. It has 3 interactive exercises: 3 find-the-move puzzles. You play every move on a board and get feedback straight away. The lesson is free.
What this lesson explains
Black's pawn just moved two squares, from d7 to d5, and landed right beside your pawn on e5. Your pawn may take it as if it had moved only one square. You move to d6, and the black pawn is removed. You may do this only on the very next move.
Recap.
Castle only if the king and rook have not moved and the path is clear.
The king may not castle out of, through or into check.
The rook may be attacked, and so may the square next to it on the queen side.
En passant: only right after the enemy pawn moved two squares beside yours.
What you practise
Black just played d7 to d5. Take it en passant.
Two black pawns stand beside your pawn on d5. One of them moved two squares last move, the other one long ago. Only one can be taken en passant. Take it.
Black is better, with a queen against your rook, and the queen attacks your pawn on e5. But Black's last move was d7 to d5. En passant moves your pawn off the 5th rank. What does that do for your rook?
Worked examples
Black just played d7 to d5. Take it en passant. En passant. Your pawn now stands on d6, and the black pawn is gone.
Two black pawns stand beside your pawn on d5. One of them moved two squares last move, the other one long ago. Only one can be taken en passant. Take it. Right. Only the pawn that has just moved two squares can be taken en passant. Now your pawn on c6 runs to a new queen.
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