The sideways curve a putt takes because the green slopes. You therefore aim at a point beside the hole rather than at it, and let gravity do the rest.
The green is where most of a round's strokes are lost — and rarely because the stroke itself was bad. Usually the line was wrong. Break is the curve the slope forces onto the ball: the steeper the tilt and the slower the ball rolls, the further it drifts to the low side. So read the landscape before you read the putt — walk behind the ball, then around to the side, and find the lowest point around the hole. The classic error is too little break combined with too little pace: the ball dies just short and falls away completely right there. Playing too much break is the kinder mistake, because a firmer putt holds a straighter line. And here is what almost everyone misses: break and pace are a pair. Change the pace and the correct line changes with it, so decide both together before you address the ball.