Each scene in a Flash movie can consist of any number of layers. As you animate, use layers to organize the components of an animation sequence and to separate animated objects so they don't erase, connect, or segment each other. If you want Flash to tween the movement of several groups or symbols at once, each must be on a separate layer. Typically, the background layer contains static artwork. Additional layers contain one separate animated object each.
Layers appear as rows in the Timeline.
When a movie has several layers, tracking and editing the objects on one or two of them can be difficult. This task is easier if you work with the content layer by layer. See Layers overview.