white has 4 pawns vs. black 2 pawns in the queen side, is that the advantage ?
According to the engine, white has some advantage,but why?

I would say that above all else, one pawn advantage here is more than one pawn advantage so to speak. Why?
It is a doubled pawn, but it is not easy to win it for black, and if that is the case, white will have a passed pawn there at some point. The last move is probably a bit bad as well, it blocks black's bishop, it restricts white f3 knight though, but that knight can be maneuvered to c4 via d2, and black can't easily kick it. Probably better is to develop that other bishop, and then go from there. Especially because white has a control of d file at the moment as well.
So potential passed pawn, a bit better pieces for white, with 1 pawn advantage should give it more than just a simple pawn advantage.

It seems like there isn't much play, but white can play b4 in this position, followed by a4, b5, and white will continue pushing the queenside pawns. If black responds accurately, they will be too passive. In this position, black just doesn't have much play, so white is better.
white to move
white is a pawn up, but engine says that white has more advantage than that,why?
If you're using Stockfish 16, 1.00 doesn't mean White's a pawn up, it means that Stockfish would give itself a 50% chance of winning if it played out the position.
This position, being a clean pawn up for White, would be a fairly easy win with perfect play; thus Stockfish's eval is higher than 1, because it's confident of winning.
thank you for your explanation
white to move
white is a pawn up, but engine says that white has more advantage than that,why?