How to win an endgame like this

Knight +2 pawns vs 3 pawns

Engine says white will win ,but I don't know how 

I think White should resign instead of wasting his or her time . It's my opinion.

according to the engine, white is winning

but I don't know how to analysis this kind of game and I don't know how to make a plan in this position

Your plan is to break the Black pawns wall, and then picking up all of them, and winning with your f2 pawn.

All you have to calculate is if Black is able to attack the f2 pawn, and here he isn't close enough.

This is done with the move h3-h4, which you can play either directly or after preparation, e.g. with the move Ng2.

You mean I can sacrifice my h pawn, as long as I can destroy Black's pawn structure and pick up them in the future , am I right?

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Gobble up the pawns then promote

So one thing to look at is coordination of the f-pawn and knight. Note currently they form a barrier at d3, e3, f3, and g3. So 1.h4 gxh4 2.Kg2. The king can just continue to run to h4 if the Black King comes across the 4th rank due to your barrier. So the only challenge is 2...Kc3. Then 3.Nf3 scoops up the first pawn. 3...Kd3 4.Nxh4 Ke2. Now almost anything wins. 5.Nf3 would be my move, heading for g1. One thing about having a single pawn and a Knight, it is about getting them in place so that the knight guards the pawn from behind. Once you maneuver in a way that the King can grab the pawns and protect the f-pawn, you abandon the knight, and since the knight guarded the pawn from behind, the King won't be able to catch the pawn once he grabs the knight. If he never goes for the knight, you can tempo Black out by triangulating your king.

Yes.

Black’s king is completely cut off, so white can win all the pawns and promote with the final pawn

nice

break down the pawn structure even when it costs you a pawn

if you lose both pawns then it is a draw

you need to play precisely to win

you can even sac your knight for two pawns if possible

well as long as it works

Wow