The power and flexibility of layers helps you in adding more depth to your artwork while giving you complete freedom to differentiate and work with separate elements in it.  
You’ll find the layers button on the top-right toolbar of both Sketch and Doodle Desks. Meanwhile, on Photo Desk the icon is located on the left toolbar.  Tap on the Layers icon to invoke the Layer Panel. The Layer Panel is where you will get a complete overview of the current layers in your canvas. The layer panel makes use of layer thumbnails to reveal a preview of each layer content on your canvas.