Layer masking is a reversible method of concealing a portion of a layer. This gives you more editing options than wiping or deleting a portion of a layer permanently. Layer masking can be used to create image composites, chop off elements for use in other documents, and restrict alterations to a portion of a layer.
If a layer doesn't have a mask, click the Add Layer Mask icon to add one. A Vector mask can be added by clicking the Add Layer Mask icon again. Alternatively, Command -click (Mac) | Control -click (Windows) the Add Layer Mask icon to add a Vector mask without first adding a Layer mask.
Clipping masks can be used to obscure parts of an image, however they require numerous layers to generate, whereas layer masks simply require one. A clipping mask is a shape that conceals other artwork while revealing only the contents of the shape.
Layer masks (rather than vector masks) are often better for photographic images because the forms in photographic images aren't as smooth and accurate as vector shapes. As a result, a little extra flexibility is frequently required.
Pixel Masks, Vector Masks, Quick Masks, Clipping Masks, and Clipping Paths are the five masking methods available in Photoshop. They all establish pixel opacities without changing the original data.