You start off by placing 3 units, two swordsmen and 1 archer. Then as time goes by, enemies start to come to attack your fort gates. You earn gold with each kill. Goal of the game is to defend and survive all the enemy waves till the end! Buy upgrades, unlock units and kill enemies trying to destroy your fort gates.
If all your gates are destroyed, you lose that wave, however you get 3 chances for each wave in each mode to retain your progress. If you lose 3 times continuously then your progress will be reset but you will get to retain the unlocked units, so that when you try it next time, it's easier.
Use mouse to click and place units on ground. Press Space bar for upgrade screen. Press P to pause the game.