For me best way to learn is study ready project, good done. You can check two Epic projects: Racing Game and Landscape Mountains (in learn tab). Here you have rocks with material where snow or sand is placed on top only, you can easy change it for grass (I think this is already in Landscape Mountains).
So you have best sample here, just import projects (free) and try.
I use similar way for my landscape, rocks and other assets, works great.