Mask
How to Use Clipping Mask in Photoshop

Launch your Adobe Photoshop and make a new document

Clipping Mask

Choose "Custom Shape Tool" on the left tools bar. It is mostly hidden click and hold on the "Rectangle Tool" and you'll see it at the bottom of the list.

Clipping Mask

From the top panel choose the custom shapes

Clipping Mask

Then, draw a shape.

Clipping Mask

Open a picture and use "Move Tool" to pull it to the file which has the shape.

Clipping Mask

Go to the layer panel, between shape layer and picture layer line move your mouse then hold Alt key and click your mouse. While you are holding Alt key the mouse turns to be like as the symbol underwater cycle like in the following picture

Clipping Mask

Then you'll see the change as below:

Clipping Mask

Use "Move Tool" to adjust the picture layer's location.

Clipping Mask

The last effect of this class is as below. So now you know use clipping mask in a photograph is so easy, isn't it?

Clipping Mask