Build a path that allows to bring the metal ball to the container. To play, you have to take pieces from the editor visible at one side and place them in the scene to fill the holes and create the required path. When it's ready, release the ball to see if it really works.
In the editor at the side there's pieces you can move to the scene: click them, then drag and drop them to the point where you want to place them; you can move and rotate the (first click the movement or rotation symbols so they look red, then click and drag to move and rotate respectively). When the path is ready, click 'Start' to get the ball rolling. When a level is successfuly completed you can go to the next by clicking 'Next level'.