Question

what is the purpose of stage and timeline

Answer 1

The stage is the large white rectangle in the center of Flash's workspace, it is like a virtual canvas. Here's where you draw the pictures, display text, and make objects move across the screen.
Any graphics placed in this area are visible to the audience watching Flash when it plays.
You can define the properties of your Stage, such as its size and color, or change the zoom (see the image below).
- The work area is the gray area surrounding the stage, the objects placed in this area don't appear in the Flash presentation.

Answer 2

I think that stage in flash is used for performing the animations