Hi Doug,
What don't you know about layers?
Take any picture, open it in Photoshop then go to Layers and Adjustment layers. Choose Levels.
Play with that and then post the picture and the layers. Can you do a screen capture? On a Mac it's Command_Shift_4 and this combo will turn the mouse pointer into a + and with that you select what you want to copy.It will appear on your desktop.
Once you realize the power of layers, you'll be so grateful and liberated.
Asher
Here's a quick intro. Try it, then
this and find more by Google searching "Photoshop Layers Tutorial".