In other words, no bullet, un-cocked and safety mechanism is on. So the only way for the user to fire the weapon is to cock the gun, which puts a round in the chamber and then this would put the weapon in condition one. So in order to cock the weapon one must rack the slide to place a round in to the chamber before ready to fire. Condition 4 would be classified as clear and safe. Which means no round in chamber, no magazine in the weapon, hammer down, and slide locked to the rear with the safety on. So there is no way to fire the weapon unless you put a magazine into the weapon, rack the weapon and pull the trigger. With that cleared up, there is a lot that happens inside the weapon when the user does decide that he/she is ready to fire the weapon.
Most people think that when you pull the trigger there is an explosion that happens inside the gun, but that is a common misconception. What actually makes a round fire is the process of the hammer being released and striking the