How to Change a Mac Desktop Background

To change your Mac's background (wallpaper), open System Settings(or Preferences) > Wallpaper, then choose from Apple's built-in options (Dynamic, Solid Colors, Photos) or click Add Folder/Photo to use your own pictures, which you can also set to shuffle or change dynamically.

Alternatively, you can right-click the desktop and select "Change Wallpaper" to go directly to these settings. 

Using System Settings (Recommended)

1. Open Settings: Click the Apple menu> System Settings (or System Preferences on older macOS).
2. Go to Wallpaper: Click on Wallpaper in the sidebar.
3. Choose a Wallpaper:
   • Dynamic Wallpapers: Adjusts to the time of day (e.g., landscapes, cityscapes).
   • Colors: Select a solid color.
   • Your Photos: Use your own pictures or add a folder of photos to shuffle.
   • Aerials: Animated aerial views of Earth.
4. Customize: Use options next to the wallpaper name to change shuffle intervals or set light/dark versions. 

Quick Method (Right-Click)

1. Right-Click Desktop.
2. Control-click (or right-click) any empty space on your desktop.
3. Select Option: Choose Change Wallpaper (or Change Desktop Background) from the menu.
4. Follow Steps: This opens the same Wallpaper settings panel where you can pick from categories or add your own images.