Windows 95/98/NT/XP users can use their right-mouse button to speed up many tasks. The term right-click and right-clicking as they are used here, refer to the action of holding your mouse over a graphic and then clicking (and holding) your right mouse button.
The option you to perform is:
"Set as Wallpaper"
Mac Users (OS 8.5) click on the thumbnail of the image you want for your desktop. Once it has finished loading, click on the image with your mouse button and scroll down to "Save this Image As" in the menu.
Save it to your hard drive or your desktop. Next, go to your Apple menu in the upper left corner, scroll down to "Control Panels" and choose "Appearance". Click on the "Desktop" tab. Click the "Place Picture..." button on the lower right and select the location where you saved your desktop image and press "Choose." Then, press the "Set Desktop" button in the Appearance menu.
Your image will appear on your desktop. (Note: on Mac OS 8.1, choose "Desktop Patterns" from the control panels instead of "Appearance").