As Leon said it is all about the speed of the putt.
There are different green speeds, which may trip you up at first, so pay attention to the speed of the green you are on and get the hang of the weight you need to hit the ball. Once you can land the ball within 2 feet of the pin consistently (2 putt consistently) you know that you've mastered the speed of the putt. At that point you can learn how to read the greens and start making those first putts more consistently.