I know how to make a snow effect but how to make an snow simulation on terrain....? I mean how can we make a real snow surface...?

when a 3rd person controller walks on the terrain his foot prints has to be placed on the terrain just like the real time snow terrains

Put colliders in the characters’ feet that leave a footprint prefab when they collide with the ground.

Or learn advanced shader programming to do it like in AAA games