Importantly, you must protect the gate and prevent zombies escape. In the game there are 6 types of weapons and 6 upgrades for each and 3 types of upgrades for tractor: life, armor and speed. You can find it in the shop. In the game there are 6 large levels with different number of gates that must be protected and a swarm of zombies. You can kill bosses and cannons and get good money for it.