Your Turret is controlled with your mouse. It has a limited range, if you are out of range the turret will automatically move. The crosshairs will also turn white when you are out of range. To fire use your left mouse button, you must press it continually, you cannot hold it down. You can pause the game at any time pressing the "P" key on your keyboard. At the end of every level you will have the option to upgrade various items.