Photoshop CS6 Tutorial
How to Use Adjustment Layers in Photoshop
Adjustment layers duplicate the function of several menu items. For instance the Levels command is available under the Image>Adjustments menu.
By adding an adjustment layer instead, you have the ability to adjust, remove, fade or change the blending mode setting at any time.
With an image open in Photoshop, click the Create Adjustment Layer icon in the Layers palette.
The Adjustment layer menu displays. Notice that most of the choices have identical names as Photoshop menu items. Select Hue/Saturation from the list.
The standard Hue, Saturation and Lightness sliders appear. Move the sliders and note the changes in the image.
Select the Colorize checkbox and adjust the sliders.
The Adjustment Layer retains your new settings.
To make adjustments to your layer, double-click the Adjustment Layer thumbnail.