Understanding Layer Masks and Clipping Masks
Be able to describe
What is the difference between a layer mask and a clipping mask?
http://www.myinkblog.com/getting-to-know-clipping-masks-and-layer-masks-in-photoshop/
Know how to
Blend two images together using a layer mask
http://www.photoshopessentials.com/basics/layers/layer-masks/
Alter and image using a layer mask and an effect
http://wegraphics.net/blog/tutorials/photoshop/photoshop-for-beginners-understanding-layer-mask/
Alter and image using a clipping mask
http://www.photoshopessentials.com/basics/clipping-masks-essentials/
Blend together text and an image using a clipping mask
http://www.howtogeek.com/57159/how-to-use-clipping-masks-in-photoshop/