I mean, when you copy paste it, it will look exactly as on shadertoy, projected on a flat surface that covers the whole screen. Yeah, that’s not very useful…
To do something meaningful with it you’d have to pass some information about your scene (camera…) to the fragment shader and then do the transformations yourself. Put it in a Filter and render it (for example) as a fullscreen effect (FilterPostProcessor).
I guess this really depends on what you want to render. You can also read the depth buffer to integrate the rendering into your scene.
The technique is called Ray Marching.
As an example:
Damn, can’t link the shader because shadertoy is down 
But it’s the first one you get when searching for “clouds”.
Essentially copy pasted into my game, just for testing. Downsampled to 1/3 for better performance (getting 400-600 FPS on GTX 1070).
Of course I’m not gonna steal this 1:1 
The goal is a volumetric Fog of War inspired by this: