How to use TerrainLayer

Hi,
Im trying to make a new terrain in HDRP 2018.3 but can't figure out how to use the TerrainLayer with the terrain object to add textures. Is it currently possible to add textures to an HDRP terrain?

 

It took me half an hour to figure out that you have to click "Create neighbor terrains" to select the texture paint mode.

 

And if you read the "Getting Started":
https://blogs.unity3d.com/2018/10/10/2018-3-terrain-update-getting-started/

... it doesn't tell you how to actually get there.

Thanks Raubhamster.