Make Ball roll without imput

Hey guys I'm brand new to all of this and learning as I go. I'm trying to make a very basic game at the moment and I'm able to get my cube(character) to move with input and dodge a couple stationary obstacles. I was hoping to make the level more challenging by adding some spheres moving from the left to the right switching directions when it hits the wall on the x-axis. I have no idea where to even begin this though, any basic direction or links to sites/videos that might help would be greatly appreciated so far all I've found is tutorials showing how to make ball move with user input.