In fps you look at a cube and point your cross hair at it and break it into pieaces

I want to make a script where when you look at a cube with your crosshair in first person shooter, you can press the left click button, and it breaks the cube into pieces

Easiest way I know with Unity, isn't that easy.

But in case no one else replies, this'll help a little.

So, you model a cube like normal. Export that as a FBX or w/e to get it in to Unity, then you take that same cube in the modeling program, and you "destroy" it, so then you have a whole copy, and a destroyed copy, then all you do is when the player shoots it, you have some kinda animation (You can animate in the modeling program), and it plays the animation, therefore making the cube broken... I'd suggest putting a puff of smoke so people don't see the actual animation, just pieces flying out, but that's a personal opinion.

Good luck!