The objective of the game is to defend your castle and attack your opponent's castle at the same time. Everytime you hit an enemy unit, you gain gold which you can spend on your own troops, building defenses and catapults, or upgrading your hero.
A tip would be to try to send your troops in tightly packed waves so they can dish out the maximum damage. The upgrade which increases your bow's attack speed is very helpful. Good luck!
Controls:
Shoot=Click and Drag the left mouse button
Look Around= W, A, S, D keys
Buy upgrades/Troops=Click on the middle panel
Run game in Super Speed Click the "S" button on the lower left edge.