Side Scroller Template Custimization?

Hey guys im a complete noob when it comes to game dev. just downloaded UE4 last night and trying to make some good android/ pc games. I do not know anything about coding or blueprints. i am learning as i go so please forgive me if this is a silly question. i am using the side scroller template. planning to make a post apocalyptic side scroller. i planed to use some type of background image for the walls, but for the floor is there anyway i can customize it as like a landscape? i would like to paint grass/moss/stone all on the floor and place trees and maybe even make pot holes. when ever i try to sculpt or paint on the floor nothing happens. i tried making a new floor with a box and a cube and a plane. but i still cant do anything to them please any advice and tips would be much appreciated.