What are layers? How do they relate to the Timeline?

What will be an ideal response?

The Timeline also controls layers, which are used to organize the content of a Flash document. A new document in Flash contains one layer. As you create an animation, you add more layers to the document. A lengthy or complex animation could have many layers. The layers are listed in a column on the left side of the Timeline. Each row represents one layer. The frames for that layer are shown to the right of the layer name. You can place different objects in the different layers. You select a layer to edit its contents.