White moves in this endgame position below. He can win the pawn at a7 with no problems at all. But if the black king reaches the square c7 at the very moment when the white king captures the black pawn the game would be a draw.
The reason is this would stop the white king from going to the vital squares b7 or b8 to be able to push the passed pawn ahead and promote it into a queen. This means, for White to win it is necessary to stop the black king from arriving at c7.
Keep in mind that the white king must not approach the pawn directly in a straight line but can approach it going in a zigzag pattern.
This makes it possible for White to fullfill both tasks at the same time. First task is to capture the black pawn and second task is to keep away the black king from the square c7.