At the start of each level you have an opportunity to build a base with supplies specific to that level. From then on out you just need to survive until the time is up... easier said than done! It's fun and easy to pull back and fire arrows from anywhere on the screen - then watch those zombies recoil from impact.
-Fight a variety of enemies from armored zombies to web-spinning, acid-spitting spiders to skeletons carrying lit bombs -Build forts using metal, wood, spikes, and explosives -Purchase and upgrade various arrows with diverse features. Some will chain your enemies together, others pierce through, and another type explodes on contact (there's more than those three).