in-game-help, iPad edition
The objective of the game is to defend your fortress from the attacking forces. If your wall's health reaches 0, you lose.
You can kill enemies by flinging them into the air or smashing them into the ground. Some enemies are stronger and take more than one hits to kill, and the siege engines and flying enemies are simply too tricky to pick up, so you'll need help killing them from your friendly units.
At the end of each round, you get gold for each enemy you kill and capture, which you can use to purchase friendly units and upgrades.