cloud sage
A clipping mask lets you use the contents of a layer to mask the layers above it. Contents of the bottom or base layer determine the masking. The non-transparent part of the base layer clips (reveals) the content of the layers above it in the clipping mask. All other content in the clipped layers are masked out (hidden).
For more information about Clipping Masks, consult the relevant sections in the Photoshop User Guide: https://helpx.adobe.com/photoshop/using/revealing-layers-clipping-masks.html
For a basic demonstration of Clipping Masks, see the following example: