Press Play in the middle of the screen. The next screen will show five weapons. However, because the four advanced weapons cost between $2800 and $8800, you will have to begin with the standard handgun at the bottom of the screen. Once you click the red Apply button to the right of it, you will be shown a screen with eight levels. Since all but the first are locked when you begin playing, that is the one you will click.
This game puts you directly in the line of fire. As a result, you have to be ready to use your mouse to aim and shoot. In addition to firing, you can use the left, right and down arrows to protect yourself from the bullets that the bad guys fire at you.
LEFT MOUSE CLICK: shoot
SPACEBAR or CTRL: reload
LEFT and RIGHT ARROW KEY or A,D: move
DOWN ARROW KEY or S: take cover