Learn how to create simple abstract desktop wallpaper.
 
Open a new file having 1024x768 px and 72 dpi.

Select a photo now, having pictured on it the sky. It must have the same sizes, mentioned above.

Create Abstract Wallpaper in Photoshop CS

Click on the next combination Ctrl+U and set the parameters from the next table:

Create Abstract Wallpaper in Photoshop CS

Add on our picture the changed sky's picture lifted up.

Create Abstract Wallpaper in Photoshop CS

Choose the instrument from here
and draw the clouds' silhouette.

Create Abstract Wallpaper in Photoshop CS

Create Abstract Wallpaper in Photoshop CS

Blending Options-Gradient Overlay

Create Abstract Wallpaper in Photoshop CS

Gradient's parameters:

Create Abstract Wallpaper in Photoshop CS

Selecting the previous instrument, it's possible to represent the next clouds' layer.

Create Abstract Wallpaper in Photoshop CS

Create Abstract Wallpaper in Photoshop CS