About Photoshop layers
Photoshop layers are like sheets of stacked acetate. You can see through transparent areas of a layer to the layers below. You move a layer to position the content on the layer, like sliding a sheet of acetate in a stack. You can also change the opacity of a layer to make content partially transparent.
Transparent areas on a layer let you see layers below.
Go to Window - Layers to show the panel.
Each layer can be named by double clicking on it. The light gray color shows that the layer is selected. The eye on the left means the layer is visible.
Opacity and Fill: both affect the transparency of the layer. Opacity is used the most.
An adjustment layer applies color and tonal adjustments to your image without permanently changing pixel values. You can discard your changes and restore the original image at any time.
Adjustment layers provide the following advantages:
Layer Mask Explanation
Layer Masks Show or Cover up what you did on the layer.
Meaning a White layer mask shows what you did to the layer. A Black layer mask covers up and conceals what you did.
Painting White or Black with a paintbrush will let you selectively cover up or show what you did.
When I painted black on the layer mask it concealed the effect of the layer, which turned the entire photo black and white.