By default, Flash loads one scene for any project. To further modularize a project, you can use additional scenes and then switch between scenes with ActionScript.
To open the scenes window, click on Window -- Panel -- Scene as shown in the screenshot.
The scene window is just another small panel that keeps track of your scenes. The scene window is shown in the image below.
To switch between scenes, you'll refer to the different scenes using the scene number or name, and then the frame number and name. For instance, if you placed a button on the second scene and you wanted clicking it to move the user to the first frame of the first scene (which is named Scene 1), you would use the ActionScript:
on (release) { gotoAndPlay ("Scene 1",1);
}