If you have ever played three-on-three half court basketball, you know that one member of your team should be the "go to" player when you need to score a basket. In chess, promoting a pawn is like scoring a basket. It moves you ahead in the game, bringing you closer to the win. For this pawn endgame, you control the white pawn team. Which of your pawns is your go-to player for promoting? Is it the a-pawn, the b-pawn, or the c-pawn? Or will it depend on how the other team plays?
Our possible first moves are 1. a6 or 1. b6 or 1. c6. Which one should we play? Which pawn is our "go-to" player? 1. a6 and 1. c6 could both win, but only if black makes the mistake of letting us capture his b7-pawn. If that happened, our newly-minted b-pawn would promote. But if black plays correctly against 1. a6 or c6, he will win, as shown below.
So that leaves 1. b6 as the other possible move. It seems risky to push this pawn, because two of our basketball-playing pawns take falls on the half court. But in the end, our remaining pawn becomes our go-to player and promotes! The key in pawn endings is not always how many pawns you have left, but who gets to promote (or queen) their pawn first. Remember that!!!
The next diagram shows the action.
Now that you have played some three-on-three, you should be more aware when opportunities arise in your game to sacrifice one pawn to promote another. Promotion may just be the basket that puts you on the road to winning your chess basketball game. After all, once you promote to a queen or to a rook, you will be able to checkmate. See BoundingOwl's articles on the King and Queen checkmate and the King and Rook checkmate for more information.