Summarize this article in one sentence.
The Apple Menu is in the left corner of the top menu bar. This will open the wallpaper and screensaver controls. By default you can choose from Apple sample wallpapers and your pictures folder.  For simplified, on-the-fly wallpaper changes, simply Ctrl + click a photo on your computer and select “Set as desktop background” from the context menu. This lacks some of the customization options of the Display Settings. This button is in the lower right corner of the window and will prompt you to browse your computer for image locations. The picture will be set as your wallpaper and can be viewed in the background. You can change the background as many times as you like by selecting other pictures in the browsing window. Once this box is checked, you can select a time interval to decide how often the wallpaper will change from the menu to the right. This option will use all of the pictures in whichever folder is selected when selecting the checkbox. This finalizes your decision once you have settled on a wallpaper choice and optional settings. The settings are auto-saved as you select them.

Summary:
Open the Apple Menu and select “System Preferences”. Click “Desktop & Screensaver”. Tap the “+” button to add pictures from another location. Click a picture to set it as your wallpaper. Select the “Change picture” checkbox to setup a wallpaper rotation (optional). Press the “X” in the upper left corner to close the window.