Layer is simply imagine one image stacked on top of another. If I set one layer as the background and paint it red for example, Then add a circle shape as another layer, text as another and a border as another the benefits are that all the layer’s are then independent of each other.
Here’s one image, I made it for the site I am working on its not finished but will give you a example the shadows are all independent layers the background consists of over 20 transparent layers.




