How do you use en passant?

Answer 1

Assuming you're talking about en passant in Chess I'll explain. Say you haven't moved a pawn and there is another pawn threatening the space one up from your pawn. Suppose you move your pawn two spaces up taking it out of harms way of your opponents pawn. En passant is when they move to the space that you would've moved to if you'd only moved the pawn up one . They take you piece and take the space you would've moved to. This move only works with pawns.

Answer 2

It can be used ONLY on your move, right after your opponent passes one of your advanced pawns with a pawn on its very first move. Your opponent has opted to move a pawn two squares ahead as its very first move. You have the option, on your very next move, of acting as if the pawn was only advanced one square, and you can capture the pawn (you capture it 'in passing') and advance your pawn to the square it would have occupied on a regular capture of that pawn. If you don't do it on your very next move, you lose the option. If an en passant capture is a player's only legal move, it must be done.