
I got the picture above using layers, masks and filters from this:

This is my nephew being goofy and trying on my new sun glasses.  He should know I always have a camera handy just to catch these embarrassing moments.  It wasn't the best picture for this assignment.  I should have found one with more shadows and highlights.  But I wanted to see what I could do with those sunglasses.  So here's what I did:
First I made a new layer coping the original.  I always do this in photoshop because I've screwed up originals  in the past.  I turned off the visibility of the original layer and made a layer mask on my copy (I call that my working base layer).  Then I selected the mask by clicking on the mask thumbnail on the layer palette.  Then on the photo I used the quick selection to select large sections of the kitchen in the background.  I used the paint bucket to paint the kitchen areas black.  That made the kitchen invisible.  I threw in a gradient background layer, just to see that I had my mask just right.

I made several copies of this image so I could play around with several versions and not have to redo the first mask.
For my next image, I put a new background behind this picture.  I use to do this kind of thing a lot using the eraser tool to get rid of cluttered backgrounds.  But the mask layer method is so much better because its not destructive.  When I realized I had masked out areas I didn't want to lose, I just went back and painted that area on the mask white which restored that part of the image.  So here's the image with a new background (from a cruise to Redoubt Bay).

Next I wanted to play with those sunglasses.  What I wanted to do was put Brian on a sunny beach and add the reflection of a girl in a bikini showing in the lenses of the glasses.  But I didn't have a good picture of a bikini clad girl.  So I settled for another scene from Redoubt Bay. I made another layer of Brian and made a mask layer of the lenses.  This was a little tricky because the glasses and the lenses are so close to the same color.  There's a little flare of light on the right lens that proved to be very problematic.  I ended up painting my mask layer with the paint brush tool rather than using selection tools.  Then I slipped in another layer between the two layers of Brian's face.  The top Brian layer had the glasses masked out so the image underneath it shows through.  I wanted to make the lens look reflective using the blend modes.  But I could never find the right one for that.  I ended up using the lighter color blend mode on the waterfall layer.

So when I finished, I thought it looks silly.  But I learned a lot about layers and mask and next time I'll pick better photos to start with.
Next I used the technique John demonstrated in his YouTube video.   I used the selections drop down menu to select and make layers of highlights, midtones, and shadows.  Then I took each layer and played around with hue, brightness, saturations and levels.  I saved several and put them together.

The top left one I saved because the skin tones look kind of bronze or golden.  I've tried to make gold before and it never looked right.  But now I have a formula for it.  Base layer flesh tone, the highlights are greenish yellow, midtones a darker green and shadows blue.   So the next time I want to turn something gold, I'll know I can do it with layers. 
On the top right, I made the shadows and midtones dark and deleted the highlights and base layer letting the background show through.  For the bottom left I was just playing with color hues, added the disco gradient, flattened all the layers and them applied the poster edge filter. 
My favorite is the lower right image.  I started with the image on the top left and I added black squares to the background layer.  I deleted the layer with the base photo of Brian, I flattened the remaining layers and applied the cutout filter (under artistic filters).  The filter settings were:  number of levels - 6, edge simplicity - 10 and edge fidelity - 2.  It's the only image I did that isn't goofy looking.  But I think it made the others worth whiled.