In Filler, your goal is simple: fill 2/3 of the level. To create a filler ball, hold down your mouse button. It will grow until you release the mouse button, it hits another filler ball, or a bouncing ball runs into it.
Hold down Mouse click to create a filler ball. Release the mouse to freeze it. You have a limited number of lives and balls each level. If you squash a bouncing ball, it will reappear at the top right corner. If a bouncing ball hits your filler ball, it will disappear and you will lose a life. If all lives are lost or you run out of filler balls it's game over.