Click on the two spheres of the same color are connected bond to collapse them. Only spheres with one or two binds can be collapsed. There is short tutorial embedded. Orbit view with left mouse button drag, zoom in and zoom out with scroll wheel. Press "R" key to reset level (or click button with "R" letter). Press "H" for taking a hint, if you don`t know what to do (or click button with "?" sighn).