Have you bothered to do any substantial research? There are hundreds of articles on how to do this in various forms.
There are even a few on this site.
Infact this one:
Howto: (Almost) Everything In Active Directory via C#[
^]
Comes top of a Google search for "c# active directy user creation" (Yes I even spelt directory wrong and it found it).
It should tell you everything you need to know.