A few ways:
If the g pawn is moved you can get a knight or bishop into an attacking area around the king. Also, if you move the h pawn up it can create a point of attack for the pawn to open lines around the king. e.g. http://www.chess.com/echess/game?id=63528502
http://www.chess.com/echess/game?id=61970168
With the h pawn mentioned it often provides a target for sacrifices, a bishop for example, especially if backed up by a queen because a recapture can often open both files infront of their king and leave it very exposed to attack.
If the f pawn is moved maybe it opens likes for a bishop to attack the sqaures around the king.
Basically the point is once a pawn moves it can't move back so it can never defend the squares it was defending.
I'm going to try to word this as accurately and simply as possible, but hopefully you guys can bear with me, since I'm very new and don't always know the terms of chess.
The scenario is this:
You opponent has commited to castling and setting up his or her defense to one side of the board. I've heard that the pawns in front of his king-side defense should stay in place and that when he has to move one of them (often up just on spot), then that weakens his king-side defense.
My question is how so? How can we exploit a person who has moved their pawn up a space in that spot.
For clarity, let's say you're WHITE and opponent is BLACK. The black opponent castles on the king-side in a formation in which he has 3 pawns in front of the king and rook and his knight is in front of the 3 pawns and the bishop is out somewhere else. This is a very typical/common defensive position. But let's say he moves the pawn that's in the corner up one spot. I've seen this being common too.
What do you do to exploit that?
[if you gys can't figure out what I mean, then I can maybe put in a game to illustrate if need be]