In Survival mode, you must right click to delete incoming hazards that threaten a small village. You get 1 point for every hazard. Not all hazards are included within survival however. Once everyone dies, you can enter your score onto the scoreboard.
Nukes, Volcanos, Zombies, Tidal Waves, Meteors, Tornados, and Lighting clouds.
(Future hazards may be added to Survival.)