Code to fire a projectile with left click

Hi,

I want to make a piece of armour that when you wear it and press left click, it fires a projectile, regardless of what's in your hand.

I'm aware that this can be done with coding with a keypress event but I am clueless when it comes to coding and I can't find any tutorials for what I need.

Can someone write the code I need to make something like this work, or at the very least, link a tutorial on how to make somethiing like this?

Thanks.