when you press play you start the game and while fighting you can press C which will fire in the direction you are facing which is determined by what the last key you pressed was for example if you last pressed the right arrow key or D key then it you would fire to you right, if you last pressed the left arrow key or A key then it you would fire to you left, if you last pressed the up arrow key or W key then it you would fire to you up and if you last pressed the down arrow key or S key then it you would fire to you down, and if you press the Space bar then a small temporary shield will appear in front of your character that will point in towards your mouse pointer and here's a little tip, just leave your mouse on the enemy.
It may be a little stressful because it sort of bar ashes you with attacks