The multiplane animation was first introduced by Walt Disney who noticed when filming an animation that specific parts, such as the moon enlarged when zooming in. This is not good, as the moon does not actually enlarge in real life, in order to make the animations seem more realistic he made planes. One plane could get bigger while the other one stayed short, thus making animations more realistic and more better.
I made mine with five layers. Since this was my first time using more than one plane I admit that I made a multitude of mistakes, the min one being accidentally painting in the wrong layer. The animation part turned out better however. The part that I started with and my favorite part was doing the sky as it turned out the best layer and looked really cool in the end. I built up from there adding a back layer, a wall layer, a medium layer and a front layer. This is how it turned out.