The king is fed up with the Goblins that have been dominating and ransacking his country for years now. That's why he asks you to kill as many Goblins as possible. In order to do so, you'll first need gold, that the miners can get from the mine. You can use this gold to hire soldiers, that can attack the Goblins. If you manage to accomplish all the missions, you might become the new leader of the kingdom!
Click on the icons at the top to hire miners and soldiers, or in order to buy upgrades.