The timeline is the area on the screen where you will be working with layers and frames to alter your movie's content and animation. A movie is a collection of frames and the timeline is the area in Flash where you will be configuring those frames (like the way a cartoon is made, with a collection of still pictures run together really fast to give the illusion of motion). Below you can see a visual description of the timeline
Current Frame: The current frame indicates the frame number whose contents are directly visible on the stage (see stage below) and is the current position of the playhead. So, what you see on the stage, when there is no movie playing, is the current frame.
Frames per second: Frames per second (or Frame rate) is the actual frames per second setting for your movie, when the movie is not playing. When the movie is playing, it dynamically shows the actual playback speed. However, frames per second and actual playback speed can differ dramatically based on the processor of the computer being used. Frames per second will always stay the same, but with a slower processor a user will view slower actual playback.
Length of Movie: The term "length of movie in seconds" may be a little deceiving. The number is actually the elapsed time between the first frame of the movie and the current frame. Depending on where you place the playhead, the number will dynamically change as well.
Playhead: The playhead allows you to select the frame to be altered. It also allows you to view the movie by scrubbing, or dragging the playhead across the timeline ruler.