Learn to change a photo's depth of field with Exposure. Its bokeh feature is used in a Photoshop workflow during this Alien Skin video tutorial.
Here is the last installment of the Superkids photo composite tutorial series. If you missed out on the other videos, check out parts 1 and 2. This video covers the last few steps of compositing in Photoshop and then we get to the good stuff: The effects.