Using the Levels or Curves adjustment masks
Photoshop and Photoshop Elements adjustments
Analyses

You have a photograph where you want to enhance the sky or the foreground but an adjustment will affect the entire landscape making part of it too "dark" or too "light" as you can see below.

This is the procedure
Look in the Option bar. When you click inside the gradient display with the mouse pointer, the gradient "editor" will pop open as seen below. Choose "Black, white."

Close the Gradient Editor by clicking "OK".
The mouse arrow will become a small "+" cursor... Now draw the gradient on the photo, (Hold down the mouse button and draw)... You'll see the gradient in the mask window in the layers palette... you might have to undo and change the direction of the gradient by clicking the reverse button in the option bar.


Gradients in Lightroom
The gradient button in the Develop Module

In the develope module. Three clicks of the mouse and you are done...
Gradients in Camera Raw CS4
The gradient button
Choose the gradient button. Three clicks of the mouse and you are done... Just like Lightroom
Class 2 Review
Keyboard shortcuts
Duplicate layer
Command + J (PC)
Control + J (Mac)
Select the Gradient tool
G key
You can assign your own keyboard shortcuts for adjustment layers. Here's a short video, It's a Photoshop Killer Tip by Matt Kloskowski at Layer's Magazine
