The objective for each level is outlined at the beginning of each level. The center HUD display can be changed to show the level map, a scope, a compass or ammo remaining.
W = Move Forward. A = Strafe Left. S = Move Back. D = Strafe Right. Left Mouse Button = Fire. Right Mouse Button = Change HUD. M = Music Off. ESC = Menu. 1 - 4 = Select Weapon.