The Timeline organizes a document's content over time in layers and frames. Like a film, Flash documents divide time into frames.
Layers are like multiple pieces of film placed on top of each another, each layer containing a different image that appears on the Stage. Layers are listed in a column on the left side of the Timeline.
Each layer's frames appear in a row to the right of the layer's name. Above the frames the Timeline displays the frame numbers. The playhead indicates the current frame displayed on the Stage. As the document plays, the playhead moves left to right through the frames in the Timeline.