https://catlikecoding.com/unity/tutorials/rendering/part-14/
Forward Fog
Up to this point, we’ve always treated light rays as if they traveled through a vacuum. This might be accurate when your scene is set in space, but otherwise light has to travel through an atmosphere or liquid. Under those circumstances, light rays can get absorbed, scattered, and reflected anywhere in space, not only when hitting a solid surface.
An accurate rendering of atmospheric interference would require an expensive volumetric approach, which is something we usually cannot afford. Instead, we’ll settle for an approximation which relies on only a few constant fog parameters. It’s known as fog, because the effect is typically used for foggy atmospheres. The visual distortions causes by clear atmospheres are usually so subtle that they can be ignored for shorter distances.
1.1 standard fog

unity’s lighting window contains a section with the scene’s fog settings. it is disabled by default. when activated, u get a default gray fog.

however, this only works for objects that are rendered using the forward rendering path.

when the deferred mode is active, this is mentioned in the fog section.
we will deal with the deferred mode later.

for now, let us focus on forward fog.

to do so, we need use forward rendering mode. u can change the global rendering mode, or force the main camera to use the desired rendering mode.

so set the camera’s rendering path to forward.

let us also disable HDR rendering for now.
create a small test scene, like a few spheres on top of a plane or cube. use unity’s default white material.