By IanB (Thanks!)
I found adjustment layers and masks totally double dutch for a long time; but once I got a handle on it, the world of photography magic really opened up to me.
I hope this gets you started.
This is done from photoshop CS3.
Open an image and open the layer pallet> window>layers> and your page will look like this.
Duplicate the layer> right click on the layer>click on duplicate; or; left click & hold and drag the layer (in the pallet) to the second from right icon and release.
Turn off back ground [bottom] layer >left click the eye.
With the top layer active (in blue) left click square with circle icon at the bottom; [third from left] you now have a layer mask attached to the layer
Now the magic: Left click the white box to make it active>select the brush tool>set to opacity to 100%>have colours set to black/white>with the black colour selected paint over part of the image and the image will disappear> select white (hit “X”) and paint over the area that disappeared and the image will return. You now have the bases for a Layer masks. You will able the added a layer mask to all new layers and erase or reduce (less opacity %) effect on any adjustment layer.
To add an Adjustment layer: left click middle icon at the bottom of layer pallet>from the panel select levels for this exercise>adjust levels TO SUIT THE PART OF IMAGE YOU WANT TO CORRECT; in this case the plane. Now add a layer mask to the LEVELS layer>left click the white box to make it active>use the black brush to erase the levels effect on the sky. If you paint over part of the plane>select white and paint in to repair.
For this image: add NEW levels adjustment lay and adjusted for the sky (the plane will not be affected) You can add as many adjustment layers you like to the image
Click on middle icon>select solid colour>reduce opacity>add a layer mask>erase with black brush the suit.
The beauty of the above is all that adjustment layers are adjustable; they can be reduced; turned off or deleted them
I often mention “soft blending layers”
Open an image
Duplicate layer>click softlight blending layer to add contrast and zapp>
I also added levels layer to lighten.
Multiply [darken]; screen [lighten] overlay & soft for zapp are best for photography use.
That should get you started in the wonderful world of adjustment layer and mask. Just fiddle around with it, write a few notes, and learn as you go.
(Thanks to IanB for this tute)