cocos3d extends cocos2d to add support for full 3D rendering, in combination with normal cocos2d 2D rendering.
Rendering of 3D objects is performed within a CC3Layer, which is a specialized cocos2d layer. In your application, you will usually create a customized subclass of CC3Layer, which you add to a CCScene, or other CCLayer, to act as a bridge between the 2D and 3D rendering.
The CC3Layer instance holds a reference to an instance of CC3Scene, which manages the 3D model objects, including loading from 3D model files, such as PowerVR POD files. You will usually create a customized subclass of CC3Scene to create and manage the objects and dynamics of your 3D scene.