Wallpapers are images from Gallery (pictures you shot with Camera, synced from Picasa, and so on), still images included with the system, and live images (such as an animation or a map that centers on your location). They take the place of the default background for your Home screens.
1. Touch & hold anywhere on a Home screen that's not occupied. A list of options appears.
2. Touch a wallpaper source:
3. To set a wallpaper, touch OK at the top of the screen (for Gallery images) or Set wallpaper.