Credit: Tip is originally from Matt Ward, thanks for the tip.
Here are the quick steps.
- Create the adjustment layer and place it just above the layer you want to adjust (for now it will apply to ALL layers below it).
- Create a Clipping Mask on the adjustment layer (either right click the layer or go to the layers menu).
- Boom. The adjustment layer should now just apply to the ONE layer that was below it.
Here is a great summary quote from Matt…
It would be much easier if they just called it “Apply to One Layer” or something like that, but the Clipping Mask functionality is much more extensive than that.