The goal of Cosmic Drop is to race your "green" ships to the bottom and land on the planet surface. A single surviving ship is enough to progress to the next level.
You can't directly control your ships movement, instead you drag the comets that have touched your ships, these are indicated by a ring and flash, other "grey" comets can not be moved. You can also use the flashing comets to destroy enemy ships, a fast swipe can destroy multiple enemies. The more comets and enemies you destroy the higher your score. The game intensifies as you earn more ships and more enemies appear. You start with 2 ships, earn an extra ship at level 5 and 10 and every 10 levels after.
If you get stuck on a level you can make it a bonus level by watching a video, you are then rewarded with 12 ships to use for that level making it easy to proceed.