Do u know some good texts about it-those who explain it in more detailed way...maybe some code and stuff like that.
My first question is, are you familar with OpenGL programming? Because once you are, scenegraphs follow naturally. You generally only feel like drawing individual polygons for so long before you start wanting the pipeline the suckers. Decontructing 3D models into their component polys for rendering after checking their visibility is the easiest way to do that.
If you want code, Java3D, Xith3D, and jMonkeyEngine are all Open Source.