:ViewportPointToRay() I dont get how to use it ?

I am confused in how to use the :ViewportPointToRay() so I know that it makes a ray of 1 stud lenght but how do I transform an UI position to a screen point so I can make the needed ray.

There is no code that I am facing an error with it it is just the ray that has random stats every time.

I realised that it depends on the game's window , so it will help to make gui elements comatible with all devices