1. Layer Basics. One of the most powerful and important features of Photoshop which makes it a superior photo composition and retouching product is the use of layers. Layers are somewhat difficult to explain but it is not a complicated concept once you visualize how layers work. You can consider a layer as an image placed on tranparent sheet which you can lay on another transparent one. Each layer is a separate image which can be modified independently without affecting images from other layers. The final image (which we see) is a view of the layer stack from the top down. The picture shown at the top left is composed by combining four separate layers. The topmost layer contains a set of horizontal lines toward the bottom of the image. The next two layers have the image of a ring and a red flower. And finally, a color background layer at the bottom of the layer stack.

Photoshop provides the Layers palette (shown below) to manage each layer present in a Photoshop document. The final image can have a completely different appearance simply by displaying or hiding one or more layers, or by rearranging the layer order of the layer stack.
Each layer is displayed with a small thumbnail and a label to help identify the layer quickly. We can show or hide a layer by turning the corresponding layer visibility on or off. The eye icon to the left of each layer controls its visibility. Depending upon the contents of each layer and its position on the layer stack, changing its visibility can completely alter the appearance of the final image.

The Layers palette in this example shows four layers labeled Lines, Ring, Flower, and Background corresponding to each layer in the layer stack as displayed above. The layer "Lines" is at the top of the stack while the layer "Background" is at the bottom. The current or selected layer is highlighted (Background). All commands and editing tools apply only to the current layer without modifying any other layers in the document. Only one layer can be selected as the current layer by clicking on its label or icon.