How do you Change the Desktop Background in the Mac Snow Leopard Operating System?

Mac OS X Snow Leopard: System Preferences

You can open up a folder and right-click or control-click on an image and say set desktop picture. And it changes right away.

How do I Change my Mac Desktop Background?

Choose Apple menu  > System Preferences.
Click Desktop & Screen Saver.
From the Desktop pane, select a folder of images on the left, then click an image on the right to change your desktop picture.

How do I Change my Background on Mac Without System Preferences?

Open the Photos app .
Find the image you want to use and right click or Ctrl+Click on it.
Select "Share" and then "Set Desktop Picture."

Why Can't I Change my Background on my Mac?

Go into System Preferences >Desktop & Screen Saver. Change the desktop to one of the defaults. Then drag the image file into the window. That should fix it.