Creating clipping masks

You can use the content of a layer to mask the layers above it. The transparent pixels of the bottom or base layer mask out the content of layers above it that are part of a clipping mask. For example, you might have a shape on one layer, a texture on the overlying layer, and some text on the topmost layer. 

If you define all three layers as part of a clipping mask, the texture and the text appear only through the shape on the base layer, and take on the opacity of the base layer.

Note that only successive layers can be included in a clipping mask. The name of the base layer in the mask is underlined, and the thumbnails for the overlying layers are indented. Additionally, the overlying layers display a clipping mask icon . The Blend Clipped Layers as Group option in the Layer Style dialog box determines whether the blending mode of the base affects the whole group or just the base