How to add materials to the landscape?

I want to paint stone slabs, but I have no idea on how to do this…right now, I have 2 materials for the landscape, which is just simply dirt and grass, but essentially I want to add a new material to the landscape. I was wondering if anyone could help me?

35044-landscape.png

Landscape Material Layer Blending in Unreal Engine | Unreal Engine Documentation - Information

Texturing a Landscape in UE4 (Unreal Engine 4) - YouTube - HowTo

The Unreal Engine 4 documentation covers all of this and Google is your friend! Please always try to find it yourself before asking, you are wasting time and space.