Hello, i want to know how to get the best graphics quality via code, including shadows effects, etc.

Seriously:

http://tutorial.3dgamestudio.net/

And where is the "Graphics" tutorial , i dont see :S

There is no graphics tutorial. Graphic quality is very subjective and depends on many different things. There are technical things that influence the quality of graphics, like the texture resolution, amount of polygons etc. but there are also a lot of other factors, like the artwork and the concept of a game. So your question cannot be answered by a tutorial or a forum post. You should learn the basics. Once you got to know the basics you will be able to answer the question you asked for yourself. That's why I recommended the tutorial.

Three Words :
HARD HARD WORK !

Even with Unreal engine, if you don't have top notch quality textures, and toop notch AAA characters, you can't make amazing graphics.

Amazing graphics is not only done by the engine :
if you cannot put a wonderfull complex 3D scenes, wonderfull characters, wonderfull 3D effects programming, you'll won't have what people call Amazing graphics

Imagine Crysis engine or UT3 engine with only low poly trees, and very low poly characters it will look bad if you target AAA realistic quality.

Well forget making Crysis, here with 3DGS the rule is :
Indie games and HARD HARD HARD WORK

So only one advice : start learning 3D and HARD WORK ONLY !