A page can contain several scenes. Each scene is the same height and width as the original page or its stage.
Pages can be browsed through the finished app, whereas scenes can be browsed through on the page. To switch between the scenes, the corresponding transition must be set in the scene control. An object can also be assigned an event that allows you to transition between scenes.
Furthermore, compositions can have their own stage. Some good examples of different uses of scenes can be found in the Purple DS Composer samples under "Video gallery", "Audio Player" and "Picture gallery".