Question about en passant

how come at move 33 in http://en.lichess.org/E5dqg9Wt/black#65 it would not let me take en passant. Is there a rule about if king is on 2nd rank or something?

It's only if your pawn is on the fourth rank.

Well, fourth rank from black's perspective. The idea is, your pawn is taking advantage of the opportunity to capture that it was denied by your opponent's pawn taking two squares. Your pawn in this game was not in a position to capture had the white pawn only moved one, so en passant does not apply.

Pawn is on the wrong square.

The idea of En Passant is to imagine the pawn that moves two squares, only moves one.

ah ok. Im very new to chess. I guess I haven't learned all the rules yet. I have only been playing about 6-7 months. Only learned the rules this year. I didn't even know castling was a thing until like march lol.

Like #4 said. And think of it as you can't pass my pawn; you have to challenge me on the diagonal square. But you're only allowed one turn to capture, if not you just gave them a passed pawn.

Yes, as #6 said, the point of this rule was designed to prevent the 2-square first move from being exploited in order to create a passed pawn. Therefore you can capture the pawn en passant (which is French for "in passing"). So basically it only applies when you have a pawn that could capture another pawn if it would move only 1 square but chooses to move 2 squares to pass by avoiding capture. On the next move (and next move only) you may capture it as if it moved only one square.

Pretty neat rule, but for some reason it takes beginners awhile to figure out how it works. I had the rule explained to me by teachers and in books for years and only really understood how it works and why it's there when I got serious about chess a few years ago. haha