What are the rules of en passant?

Hey, I was playing a match of chess and this guy captured one of my pieces really weirdly with a pawn, my friend tells me it was called en passant. What are the rules of this move?

https://www.chess.com/lessons/playing-the-game

Not sure if that is locked behind a paywall, so adding to that, EP is when you move a pawn 2 spaces (first time it moves only) and in doing so, end up side by side with an enemy pawn.  On the very next move only, the enemy pawn can take it as if it only moved one square.  That is all.  

It can't take pieces.  It can't happen if you wait a few moves.  It is just an extra rule to prevent exploiting the 2 move pawn later in the game to get a passed pawn on the sly. 

Ah, that makes sense

https://www.chess.com/terms/en-passant

Yeah, it is legal. When the opponent moves his pawn two squares and you have a pawn at the right or left you can attack the pawn by this weird move. I use it very rarely.

https://www.youtube.com/watch?v=1q7lZilVy04