Well, what can I say? I also tried to help for a starting pint but you won find it. Try posting specific question. In anyway, here is my aport.
When download the jpct api you will find a folder called LIB, inside that folder you have the jpct and the lwjgl. JPCT contains this engine is mostly used to load 3DS files, render by software, manage events and all the stuff for making your game. LWJGL is an API provided for a third party. Are Open GL libraries for java. jpct also use lwjgl to render in opengl.
well, a fast review of the most important classes.
World is the class that contains the lights, maps, objects3D and everything. Its like an enviroment in which you build all your 3d files and manage the lights.
TextureManager used to handle the textures of your maps.
KeyMapper is used to get the key events inside a game
FrameBuffer is used to asign the render type, resolution and things like that.
Loader is a class that contains the information to load 3d files like 3DS, MD2 and some others.
well. I think that this may helped you to understand better the examples sources. try reviewing them and understanding what they do. Also try to do own modifications to the FPS demo to change little thing and notice changes.
For any further help we are a community trying to help everybody here.