Here lets you choose between two different types of backgrounds
Fixed: the image you pick for the background is fixed to your view of the room. Wherever you look in the room (by moving or scrolling), the background image follows. This means that any object you place in the room does not have an absolute position relative to the background image (i.e., if you have a background of a tree and put a monkey GIF in a branch, when you move around, that monkey will move off the branch)
Fixed Background — the monkey is not "pinned" to the branch; it has no absolute position on the background image
Scrolling: you scroll across the background as you move in a room. This means that any object you place in the room has an absolute position relative to the background image (i.e., if you have a background of a tree and put a monkey GIF in a branch, that monkey stays in the branch regardless of where you move to in the room)
Scrolling Background — the monkey is "pinned" to the branch; wherever you move, the monkey maintains its position on the tree branch