This hour took an important leap forward in your game development path by guiding you through the design and development of a basic game engine for Windows games. You learned about the importance of a game engine, as well as what code goes into creating a fully functioning game engine. Although features certainly need to be added to the game engine to make it more powerful, the elements are in place for creating Windows games with much less effort than if you didn't create the engine. It's okay if you don't fully appreciate the role of the game engine in making your life easier as a game programmer. But trust me; you will eventually come to appreciate the game engine for how it simplifies game development and allows you to focus on the most important facets of game design.
Hour 4 finally explains the mysteries behind the graphics code that you've seen in both the Skeleton and Game Skeleton program examples. You learn some of the fundamental graphics techniques that will carry you forward throughout the rest of the book. You also get to create a pretty neat example program that demonstrates your new graphics knowledge.