You can control the animation by moving your hand above the Leap Motion Controller. As you move your hand, the animation changes speed a bit. When you pull your hand out of the Leap device's view, the grid transitions to a different amount of curviness. The faster you move your hand, the more the animation changes. The gauge in the secondary window indicates when your hand is being detected by the Leap device and how much the animation will change when you pull your hand away.
When you start the composition, the first thing you should do is wave your hand really fast over the Leap. This calibrates the composition by defining the range of fast vs. slow movements.