How can I make a gun shoot and apply damage to the target?

I am trying to make it shoot rapidly. For some reason the scripts from the Unity's "FPS Tutorial" doesn't apply damage for me. Only muzzle flash appears. I'm sure there are other ways. For now I'm okay with "Fire1" and "Fire2", even tho I am developing for iOS. I'll study how to simulate the mouse clicks with on-screen buttons later, but if anyone knows, please tell me. But the main question is how can I make a gun shoot and apply damage to the target?