Layers

Advanced Timeline stacks the scene in rows. Content layers hold the drawings. Each one has a name, an eye to show or hide it, a lock, and an opacity. Drag a layer to reorder it. The row menu can duplicate or delete it.

The free edition includes three content layers. Motion Monster Studio removes that limit. Add a layer with the button at the top left of the timeline.

Under the content layers, the timeline also has rows for the camera, the background, effects, and sound. Expand a layer to see its layer effects, and expand Sound to see each clip. Effects themselves are covered in Effects, and sound in Audio.