Destroy gameobject with clicking them.code prob

Hello… i know that this topic has been asked lot times in unity answers but i cant understand exactly how i have to do it and what i do wrong.

my code:

if (Input.GetKey("Fire1"))

i want to click objects with left click i think left is Fire1 and destroy them…
first of all i dont know where to atach this script?:S and second is anything else i have to do with my code… is there any other way to make it happen without castray at camera?(i checked a tut about it)

All you need to do is put this code on the game object you want to destroy.

function OnMouseDown (){
    Destroy(gameObject); //Destroys the object the script is attached to.