The point of the game is to survive and build the Flying castle, leave the danger zone full of zombies.
Collect more resources (wood, wool, stone, pelt) to build the Flying castle (wings, balloon, castle weapon, etc). The more resources you collect the more quickly you will build the Flying castle and leave the zone full of zombies. The more boxes you will destroy the more quickly you will be able to buy better weapon.
The Flying castle also will help you to kill zombies.
Collect and use stars to upgrade your abilities (speed, lives and magnet).