Displacement

I am trying to add Mulch to a drawing and I just stumbled upon the displacement area.  I took a shot at it, but it only ended up white, I'm sure I am doing something stupidly wrong, but I also am working a lot with Cultured Stone piers and I think that displacement would make the renderings look a lot better with that.  Can someone give me some step by step instructions for displacement, for both mulch and stone. 

ALSO can you set "displacement" to show "brick stepping"  I am rendering an existing building and after "building" the wall and everything around it I noticed that every 2' or so the brick steps back an inch, I don't want to have to go back and rebuild the wall.  Can this help me?

Attached is the Image I am working on.