You should to grab two or more balls the same color, and release them at the same time. You cant suppose that on the screen the number of spheres was more resolved. In the Right top part of the screen you can see point "overflow x/y" where x - current quantity of spheres on the screen, y - the resolved number. For bomb explosion, simply click on it, it appears instead of the last ball, if you have it. In order to get the bomb, just collecting a set of bonus stars.