There are five primary elements when setting a room background
Image: the picture you want for the background
Type: Fixed rooms mean that the background image is fixed to your view of the room, sort of like the image backlights the room for you. Scrolling rooms mean that as you move across a room, the image scrolls (and you can actually reach the end of the image). Objects in Fixed Rooms do not have any absolute position relative to the background while Scrolling Rooms do. (Learn more about Fixed and Scrolling Backgrounds in the previous article)
Layout (Scrolling Backgrounds Only): Centered layout puts the background in the center of the room. Tiled layout repeats the image in a pattern
Size (Scrolling Backgrounds Only): This sets the size of the image
Color (Scrolling Backgrounds Only): Set the color of the space around the image in the room (i.e., the apron)