After game is loaded press space button to open menu. Choose "New Game" and click enter. Select difficulty level and start doom game. Move with arrow keys and ctrl key to fire. Space key to open doors and shift key to run. Change your weapon with "1,2,3,4,5,6,7" keys. There are so many alien kinds. You can develope your own speacial tactics to each aliens. Be careful, this game makes dependency. :)