"To add a background" means to place an image, color, or pattern behind something else, like a picture or text, in order to enhance its appearance or provide context. Full definition
Further, there is a Story feature that lets users create various stories from their previous memories by adding background music and easily share them on social networks. (gadgets.ndtv.com)
You can even change the clock style and add a background image in different colors. (digitaltrends.com)
Switch it up by adding a background color in just one click and change the mood of your page. (neowin.net)