What is the ideal pawn structure?

People are always talking about the importance of pawn structure and how it affects the movement of your pieces and the game in general. I understand pawn structure sometimes blocks up your pieces, for example all your pawns on dark squares can block up your dark-squared bishop? But how does it affect the game in general? What is a 'good' pawn structure, and how does it leads to a win?

It's sort of like asking what's an ideal vehicle for travel.

Well it depends. Are you traveling through the desert? Across the ocean? Through the mountains? Are you just going a few blocks to buy some food? Sometimes a bicycle is best. Sometimes a helicopter.

So in chess, it depends on everything else in the position. As you said many pawns on dark squares may block your dark square bishop. So that would be bad... unless your only piece is a light square bishop, then it's ideal.

Black is winning in the diagram below

Same pawn structure, but white is now winning in the diagram below

There are different things that can make a pawn structure good.

One of them is not blocking pieces like bishops, but usually when someone calls a pawn structure bad there are more long term implications. Pawns are doubled or backwards or isolated. Pawns aren't mobile, or give poor protection to the king.

If a good structure vs a bad structure leads to a win it's usually because pawns in the bad structure are vulnerable to attack and will be lost, or don't give cover to the king, so the king is checkmated, or maybe the good structure is mobile and can advance its majority to make a passed pawn.

For example

White has a pawn majority on the kingside. 4 vs 3

Black has a pawn majority on the queenside 4 vs 3.

However black has 2 c pawns. So it's not possible for black's majority to force a passed pawn in the endgame. This by itself is usually not enough for white to win, but it's an important factor. If another defect occurs during the game (like a bad minor piece) then that plus the bad structure can be enough to tip the game in white's favor.

So while black was unable to make a passed pawn, white was able to get a passed pawn on any file (if black did nothing but wait).

Of course this is not a real game, just an example of how a pawn majority by itself can create a passed pawn if the structure is good, and how a bad structure cannot.

However even in a real game, if the last diagram were the starting position, white is winning this king and pawn endgame solely because the pawns.