Just to clarify on what Binary said, OpenGL is what you will use to actually draw your model in-game. OpenGL is by no means a 3D modelling program. In a loose explanation, OpenGL is an API that takes pre-made models on screen.using your graphics card. For starters, you need to look into 3D Modelling, which is the process of making the hi-def models. The best free program for doing this is called Blender 3D. You can also look at Maya and 3DS max, but those cost money and are very expensive.