You are a god or something, and have to defend your castle by throwing the enimes around. As you get more points, you can buy upgrades, like temples to convert the enemies, and archery ranges.
It gets super-tought at level 14, that’s when the giants arrive. You can’t pick those guys up, you must rely on arhcers or bombs or spells.
My advice? Get a temple as early as possible and train some archers, then a workplace for fixer-dudes.