How to add specific factors

Hello,I’m still learning and studying UE4.
I could use any help with post processing and vfx effects
Take a look at this video

I know,this is years of experience,and it can’t be done by amateur,but how do I make landscape look like that? I’m not asking about objects,I’m asking how to add those effects that are already on landscape. Fog details,better rendering etc.
I still don’t know how to explain it,but if you take good look at video you will see it.

The fog details are done by a applying a subtle cloud / fog texture to a single 2 polygon plane then placing that plane between objects and such. I think there’s also some smarter shader at play on those effects though, since it doesn’t look like the texture’s clipping into objects very sharply.

I probably won’t recommend these techniques in a 3D environment that the player can freely explore, they look good when the camera is stationary but won’t look good when the camera’s moving.