here is the beginning of the game I played : 1 e4. e5 2 Nf3. Nc6 3 Bc4 Nf6 4 Nc3 a6 5 Ng5. d5 6 e x d5. Be7 7 d x c6. O-O 8 Qf3. b5 then, I wanted to play 9 c x b5 (en passant), but i couldn't and played 9 Bb3 instead. it didn't prevent me from winning the game, but still, I am a bit frustrated. is anyone able to explain me why ? I would be grateful. thanks in advance
why couldn't I take "en passant" ?

here is the link to my play : Jetez un coup d'oeil à cette #chess partie: lekicars vs ouf27 - http://www.chess.com/livechess/game?id=1267462568

Your pawn has to be on the rank that the opposition pawn advances two ranks to reach. You can't take en passant from the position that your pawn was in.
The idea of en-passant came in alongside the change to allow pawns to move 2 squares on their first move. En passant was added because of the fact this 2-square move addition takes away the possibility of capturing as would have been the case if he'd just moved one square.
In your case you would not have been able to capture if he'd moved one square so you also can't capture en-passant for the same reason.
Somebody will probably explain that more succinctly though!
Well the white pawn on c6 is on the wrong square!
It needs to be on c5 to be able to capture the b5 pawn en passant.
Here is a definition of en passant:
It is a special pawn capture, that can only occur immediately after a pawn moves two ranks forward from its starting position, and an enemy pawn could have captured it had the pawn moved only one square forward.

That isn't en passant. It's an illegal move. If your pawn was on c5, en passant would've been possible, but it was on c6. En passant is a special type of pawn capture that can only occur immediately after a pawn moves two ranks forward from its starting position, and an enemy pawn could have captured it had the pawn moved only one square forward.

Oki, i understand now the slight difference there is between c5 and c6. thanks for your quick reactions
hello guys,