So i cut the steerer tube the lenght i want it and o just push the star nut in the desired distance?

IE, Im cutting the steerer the same distance as my current fork, From there, i get my measureing device and find out the depth of the star nut. and i just match it?

That would work correct?

What tools do i need to put in the star nut,

You could use a mallet to tap the star nut into the steerer. Screw in the headset bolt into the star nut and tap lightly, make sure the star nut is straight when it goes in.

Or you could just buy a compression plug.

EDIT: You could even ride without a star nut.

https://sheldonbrown.com/handsup.html#threadless

A compression ring? Is that the plastic piece that holds in my fork when i drop the stem and brakes? I have to tap out the fork with a mallet every time.

I think i'll get a star nut ):

I bought a tool for it, but you could use a socket that is fairly the same inner diameter of the steerer and hammer it down.

No plug, as in to a plug your drain or your mouth when you talk nonsense here.... anyways think the compression plug as a top cap but with integrated star nut functionality; as when it's screw is tightened, it's wedges expand upon the steerer tube, holding in place, just as a starnut would. From your point of understanding I doubt you've ever owned a bike whose fork has a carbon steerer tube.

What material is the steerer?
If it's steel or aluminum use a star nut. I just threaded the top cap bolt in a little and drove it down with a mallet.
If the steerer is carbon fiber, you must use a compression plug.

My road bike has a carbon fiber fork, But the steerer is AL I have a star nut in there.

thats how i did mine

FWIW, I've been using a compression plug on my Mark V for the past week and I am still fine.