Azgornia Unite is a Tower Defense game. You just need to place towers in order to stop the enemy rams from getting your gold. You can place a tower by clicking somewhere in the grass. Each tower though, costs you 75 gold. By killing an enemy ram, you get 25 gold. You have to take care of your gold, because if it reaches 0, you lose. You can press C to see the coordinates of the map and where exactly you can place towers.