How do i add default terrain textures to a terrain?

Hi, i am trying to make a field in BeamNG, but the thing i don't get is how do people add the grass texture onto terrains. Note: this is not a custom map, i just added a new terrain on-top of grid small pure.

 

I know how to get the grass texture, but i forget where is the button to do that

 

If you look at the tools on the top of the screen. The one highlighted that has the blue, green and red arrows that you can move objects around with if you click on the one that looks like a paintbrush, that is what you're looking for.

Once you click the paintbrush, the different textures should pop up on the right side of the screen in a box you can click on.

 

i only have warning material and the other stuff