I'm new to the program and have learned much but just can't understand one thing. Maybe someone could explain.

Lets say I open an image, duplicate layer, make adjustment layer and adjust "levels", open new adjustment layer and adjust "contrast", and then create a new layer to spot heal the face on a portrait. The new layer is "transparent" and there is nothing I can do to fix the earlier blemishes. Now, I know I can do a "Cntrl+Alt+Shift+E" and combine all layers and make a new one that I can edit. But what if I want to go back later and "re-edit" something that is under that layer where I did the "Cntrl+Alt+Shift+E" layer. If I go back and edit it, nothing changes above it. I thought layers would allow me to go back and edit changes like this along the way. It sure would be handy. Lets say I do a pix and the receiver of the pix thinks the teeth were over brightened. Do I need to now darken the teeth up? Why can't I go back? Suppose I edit pixs in the future and I need to go back to do those teeth. I would now have to redo the whole process over again from that point because of my "Cntrl+Alt+Shift+E" layers.

I guess my question comes down to ... Is there a way to make a layer that adjust all layers below, leaves layers below also editable, and is not "transparent"?

I hope this question makes sense. THANKS in advance.

Your observations are correct... once the "Cntrl+Alt+Shift+E" operation is complete, modifying anything below the merged layer has no direct effect on the merged layer or any layers above it.

re: Is there a way to make a layer that adjust all layers below, leaves layers below also editable, and is not "transparent"?

No, but it would be a neat if it worked that way...

One approach is to apply modifications/corrections/edits to individual layers first, then add the adjustment layers -- and avoid doing the interim "Cntrl+Alt+Shift+E" layers. That way you can fine tune any of the individual layers or adjustment layers after the fact w/o having to rework interim merged layers.

re: Whitening teeth trick (Scott Kelby method)
* Press Q and use Quick Mask to "paint" a selection for the teeth. When selection is painted press Q again to exit Quick Mask.
* With the selection active create a Hue/Sat adjustment layer. (Note black mask with white where teeth are located. The mask 'isolates' the effect you're about to apply.)
* From dropdown menu, choose 'Yellow'
* Move Saturation control left to remove most, but not all of yellow
* Move Lightness control right a touch to brighten
* Click OK when you're happy with the result.
* Zoom out... fine tune Opacity if needed.

Easy to adjust later, too. :)

Thanks Danny.

I've been doing much reading and nobody really brings up this point. They just go thru and show features but not "real world" workflow" and problems you might encounter. Just prior to your response, I located some videos on YouTube that seemed to help by "PhotoShop Mama." She has a workflow just like you were writing about that does most of the edits through adjustment layers that seems to work best for later edits.

THANKS again.

savage,
If you are retouching with the Healing Brush just select "Sample: Current and Below" option and work in a new empty layer (either under or over the adjustment layers).