Drag back from the red ball and let go to launch it like a slingshot into the bubbles.
Bubbles keep spawning on their own. Clear every one off the screen before a new one spawns in, and you level up — each level makes new bubbles appear faster. There's no limit to how far you can go.
Don't fall behind: if the bubbles ever fill the screen so the ball can't move, it's game over.
The bubbles filled the screen.