Photoshop layers are a like the digital version of a stack of acetate sheets within an image. They allow us to work on photos in a non-destructive manner, in other words, without modifying the original pixels of the image. They can be useful for several different things: for instance, to create a composition with several images, add text, add shapes with vector graphics… Furthermore, applying a layer style simplifies the addition of special effects such as parallel shadows or any kind of shine.
Working with Photoshop layers makes editing much more flexible, being able to place the contents of our choice or change the opacity to make the layer more or less transparent.
With regard to how they’re organized, we must remind you that each new image only has one layer. The issue is that that number, the group of layers, and the effects that can be additionally applied are only limited by our computer’s memory.
To work with layers, we have to access the Layers panel. From there can manage the groups that allow us to sort them in a logical manner to improve the organization of the user’s work.
In turn, there are also elements called Adjustment layers. The latter seem to be bare of contents but can really be used to adjust the colors or tones that affect lower layers. That’s what we were referring to with non-destructive editing since we can modify certain parameters of the image respecting the original pixels.
We also have to mention the so-called smart objects which are a special kind of layer that contain at least one layer of contents. They can also be transformed without modifying the pixels and we can even work on them as if they were independent images.