how to create a new layer for painting the landscape?

I want to paint mossy grass and some more different layers on my map.
I need someone who can explain to me what I have to do for making a new layer.
Ive watched bricks video, but…doesnt explain much for new layers.
I have created materials and textures for a new layer, now how to get those textures/materials onto a new layer?
Ive clicked on the “+” button to create a new layer, and got a blue file with settings
from here i dont know what to do…
pls help

bumping for the bump

Or a link for a good tutorial on that?