Why are you supposed to attack in the direction that your pawns point?

i dont realy know about that rule but i ulsy go for meteral not stargey

I don't understand. A Q side attack in that position seems realistic to me. You can put pressure on the b2 pawn by taking the b file and maybe make use of the b3 and a4 squares. The real problem is that white can bring his knight to d4 when you have to think twice about playing ...e5 since d5 becomes a little weak. In this case the b3 square would cover the d4 square if needed and is just a good square. It blocks the b file, but at any moment it could move with great effect if you have doubled rooks there.

...f5 is not necessarily bad here, but first it's more natrual to play on the q side and second it's not so much he attacks your weakened king, but the e5 square is now a hole. Fortunately right now it doesn't seem to matter, but it could in maybe an endgame, and since you don't have a lot of piece support it's not a very strong attack. Your opponent put his knight on d4 too soon and then blundered mate for your attack to succeed.

Oh, I totally forgot about the d3 square! Now that square is a fantastic one, as it also attacks b2.

I think 18...f5 is a great move, since it prevents e3-e4 which is the only way for White to get any counterplay. He probably should have played 19.Nd4 with the idea of b2-b4 trying to exchange his weak pawn. I don't like your 19...Bb8 - this square should be left free for your f8 rook. That's why 19...Be7 is better, but I would also consider 19...Qd7 - let him take the bishop and after 20.Nxd6 Qxd6 you have an excellent position with a simple plan to follow - doubling your rooks on "b" file. I don't see any plan for White to defend his Pb2.

As I understand it, that "rule" only applies when the center is locked or you control the center - and of course, in chess, there are always exceptions to every "rule."

In the position after 18. 0-0, it does appear to me that you have enough of a grip on the center for a queenside attack, but you would need to be wary of attempts by White to counterattack there.  It looks to me like you have some good chances on the Queenside once you get your other rook and queen on the b-file.  Combined with placing your knight on b3 to help control d2, d4, and c2, you should have a good attack.  Like I said, you just have to make sure that White can't counterattack in the center.  The Nb3 will help with that, at least until White moves a knight over to d2 or d4 to dislodge it.  But after that, you may be able to get your Rooks doubled on the b-file with one on b8 and the other on b3.  I forsee a future position where your knight and one of his are off the board, you have rooks on b3 and b8, your queen is on b6, and your bishop is on e5 (maybe f6).  With White then focusing on defending b2, you could launch a pawn strike down the center with e5 and d4.

My main concern was his "pawn shield" on the queen side. He only had two pawns, but how was I going to take them, with my rook? That seems like a good way to lose material. I also couldn't advance any of my pawns in the center because that would break the pawn chain and leave me with an isolated pawn.

I didn't want to move the bishop back to the eighth rank, but I didn't feel I had a choice because otherwise he would take it, trading my good bishop that aimed directly at his king for one of his knights which were kind of wandering aimlessly. It blocks the rook, but I figured eventually the rook would either be lifted for doubling or to attack the knight, or my kingside attack would fail and i would have to attack on the queenside anyway, in which case my rook was exactly where it should be.

I also figured I could move my knight up to a nice outpost square at my leisure, but doing so wouldn't directly attack anything so I didn't want to play that as a waiting move.

Anyway, that's what I was thinking.

My main question, though, is how do you break through pawns using pieces? As I mentioned earlier, it's incredibly difficult to take a pawn with a rook, for example, because you are immediately down on the exchange. I didn't have any pawns left on the queenside with which to break through.

(PS The computer analysis finished, and pretty much the last 10 moves of the game, including my speculative bishop retreat and my f5 pawn move, were all within 0.5 pawns and considered a draw by the computer, so I feel good knowing that I didn't miss anything obvious.)

Forget about attacking his castle. You have a much bigger advantage on the queen side so that's where you should play. After 19...Qd7 20.Nxd6 Qxd6 Black wins very simply by just doubling his rooks on "b" file with the idea of Nd3. White's only defence after Nd3 is b2-b4 but it weakens Pa3, which can be easily taken by doubling black rooks on the "a" file.

But aren't white's two rooks, queen, and knight a perfectly adequate defense for the b-pawn?

The "attack in the direction your pawns are pointing" is not a "rule" it's advice.  A rule is:  "you can't castle out of check", or: "a pawn may advance 2 squares on it's first move".

The reason for this advice is that one will tend to be able maneuver one's pieces most effectively where there is an advantage in space.  I disagree that this is only true for "closed" positions.  It's just that open or semi-open positions tend to be more volitale and so there is often more tactical danger to catch you if you're napping while being too involved in any purely dogmatic approach to your game. 

So, attack in the direction of your pawns if that's the best plan, but stay alert and always look for the best move...such as QxP mate!

Well, of course White may move his knight to d1, but that's exactly what you want in this position. For example, 19...Qd7 20.Nxd6 Qxd6 21.Nd4 Rfb8 22.Ne2 Rb6 23.Rfb1 Rab8 24.Nc3 Nd3 25.Nd1 and all white pieces are badly misplaced. Since all White's pieces are on the queen side, now is the right time to launch an attack on the king side by playing 25...f4.

You Generally attack in the direction that the Centre Pawns point.

But I emphasise that is a very general rule

Why is this even a question? Quite clearly you have an advantage on the queenside and no prospects on the kingside. 

ROFLMAO.

Other people have mentioned that you can control the b file with the idea of bringing your knight to b3. Instead of 18. ... Rb8, how about Qb6? This gives you space to develop both rook freely and begins coordinating pressure on the b3-b2 squares. If white responds by putting a rook at b1, black has several options: Offer a queen exchange with Qb3, advance your knight and open up multiple diagonals with Nb3, or develop your rooks. White can't play b4 because black captures en passant and gains a dangerous passed pawn. The only way I can see white coordinating a defense for the b3 square is Nd4. For that reason, you might have played 18. ... Qb8, which coordinates your bishop and queen on the h2 square. This discourages white from playing Nd4, because that would allow to safely capture at Bxh2, breaking apart his kingside. I realize the point of this discussion is to find good queenside attacks to reaffirm the pawn rule, but if white keeps his knight at f3 to protect the h pawn, you've effectively weakened his queenside defenses, plus your queen is still on the b file to assist the queenside attack. So by threatening a kingside attack, you can strengthen your queenside attack! I suppose at some point white might play g3, but this would essentially waste a turn that could have been spent defending against the mounting queenside pressure.

black could easily win the b pawn probably triple up on b file with rb6,rb7,qb8 and ND3