Sorry I need to translate the documentation of tkz-graph. First hte main idea of this package is to provide useful and simple macros and styles to the users. Finally you have two style to know : VertexStyle and EdgeStyle. When you want to draw a graph, you can choice a "general" style with \GraphInit[vstyle=Classic]. This is useful if all your graphs have the same presentation and if inside a graphe, all the vertices have the same style. But you can change the style globally by hand and you can change locally the style.
There are some inconsistency but I need to adapt tkz-graph to pgf 2.1 and pgfkeys. With the new version, I will use only pgfkeys and I will add an english doc.
\documentclass[]{article}
\usepackage{tkz-graph}
\begin{document}
\begin{tikzpicture}
% the next line is because you want the style classic for most of the vertices
% if you can't find a style in the predefined styles then you create a style with
% \tikzset{VertexStyle/.style= ....
% if a predefined style is not exactly what you want you can use after the next line
% %\tikzset{VertexStyle/.append style = .....
% You also use : \SetUpVertex \SetUpVertex[FillColor=red]
% \SetUpVertex is to avoid the use of \tikzset{VertexStyle/.append style ....
\GraphInit[vstyle=Classic]
\SetUpVertex[FillColor=blue!30]
\Vertex{A}
% with a scope you apply locally a new style but you can use a tex group {....} instead.
\begin{scope}[VertexStyle/.append style = {minimum size = 5pt,
inner sep = 0pt,
color=green}]
\Vertex[x=4,y=2]{B}
\end{scope}
% here I use \tikzset
\tikzset{VertexStyle/.append style={rectangle}}
% Now if I want to put the label inside the vertex, I need to pass the style in the
% options of Vertex with ,LabelOut=false.
% Logically, it's possible with \SetUpVertex but ...
\Vertex[x=4,y=-2,LabelOut=false]{C}
\end{tikzpicture}
\end{document}
Conclusion
tkz-graph is useful if you want always the same type of graphs. There is some difficulties to
if graphs ara not "homogeneous".
