Layers help you organize the artwork in your document. You can draw and edit objects on one layer without affecting objects on another layer. In areas of the Stage with nothing on a layer, you can see through it to the layers below.
To draw, paint, or otherwise modify a layer or folder, select the layer in the Timeline to make it active. A pencil icon next to a layer or folder name in the Timeline indicates that the layer or folder is active. Only one layer can be active at a time (although more than one layer can be selected at a time).
When you create a Flash Professional document, it contains only one layer. To organize the artwork, animation, and other elements in your document, add more layers. You can also hide, lock, or rearrange layers. The number of layers you can create is limited only by your computer’s memory, and layers do not increase the file size of your published SWF file. Only the objects you place into layers add to the file size.
To organize and manage layers, create layer folders and place layers in them. You can expand or collapse layer folders in the Timeline without affecting what you see on the Stage. Use separate layers or folders for sound files, ActionScript, frame labels, and frame comments. This helps you find these items quickly to edit them.
To help create sophisticated effects, use special guide layers to make drawing and editing easier, and to make mask layers.
There are five types of layers you can use in Flash: