cocos2d(二) scenes, layers, and nodes

    Cocos2D games are made up of scenes (CCScenes), and the director (CCDirector)
is responsible for running scenes. The Cocos2D Director runs only one scene at a
time.

    Each scene in Cocos2D consists of one or more layers, which are composited on top
of each other. For example, in building Space Viking you will create two layers in the
first scene: one on the bottom to contain the background, and one on the top to con-
tain the moving characters and action.

   Each layer ( CCLayer) can in turn have sprites (CCSprite), labels ( CCLabel),
and other objects you want to display onscreen. If you remember, when you added
SpaceCargoShip, you created a new sprite and then added it as a child of the layer.