recreating this shader effect in react-three-fiber

[pipje2001]

I am trying to use the volumetric shader from this example to work in react-three-fiber
https://codepen.io/peterhry/pen/egzjGR?editors=0010

But sadly i am completely lost on how that example even works.
I am currently trying to have simple plane which is illuminated using the shader effect used in the example.
But i just dont understand what is happening no matter how long i look at it

Could anyone point me in the right direction as to how it works?

Edit 1: I know this is not really a good question, but i am really stuck as to how it works so any help would really be appreciated!