Pawn play

One facet of my game that I have little knowledge of is pawn play. This morning I analyzed a game and Stockfish recommended playing b4 after having completed my development. Why play this move at this precise moment, I didn't see why. What reading would help me understand this kind of move and the global use of the pawns at my level? Thanks

More precisly move 13 white

Why I bought this book at a chess shop in Bologna, Italy whilst on a short city trip, is a long story, but I have just started going through this one:

"Small Steps to Giant Improvement: Master Pawn Play in Chess" by Sam Shankland
Part I Pawns Can't Move Backwards
Part II Compelling Enemy Pawns Forward
Part III Pawns Seldon Move Sideways
Part IV Compelling Enemy Pawns Sideways

Just one of many reviews after a little web search e.g. can be found here:
chessniti.com/book-review-small-steps-to-giant-improvement-by-sam-shankland/

The title of Part I seems obvious, but it was what took my attention. In the introduction the author adds that misplaced pieces can be put back on their original squares (at the cost of one or more tempi) but pawns cannot. That's why a pawn move error can have significant impact, since by nature it is irreversible. Good starting point to dive into pawn play, I thought.

When ever you question your game, do a chess analysis of it. Your game has not been analysed. Start there. Then play other moves that the engine did not propose to understand why the engine proposed a move. When you cannot see the worst moves, it makes it hard to see the good ones.

Once the kings has castled and the pieces have mobility, a pawn break is good to open up a file for the rooks.

Once the kings has castled and the pieces have mobility, a pawn break is good to open up a file for the rooks.
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