Move the mouse quickly, and the sword point will slice across the screen, dividing unfortunate bubbles in two. Move it slowly, and you can nudge a bubble in whichever direction you please, though this is a much more difficult maneuver. Once you have charged your power strike, execute it by holding the mouse button and slashing.
Each level presents you with a single giant bubble, but your attacks will subdivide it like a wobbly translucent asteroid until you are faced with a screen-full of little bubble fragments. Once they are small enough, a final strike will shatter them into harmless snowflakes. Clear the screen to advance. After a few levels, you gain access to a new weapon, a sort of heavy yo-yo on an elastic band that will leap about the bottom of the screen like a deadly puppy. To use it, catch its ring-shaped handle with the mouse button and heave it towards the encroaching bubbles. On release, spinning blades will sprout from the yo-yo's core and massacre any bubble under a certain size that dares to stand in its way.