How to find Roles in Active Directory

Question

I had connect my application to active Directory but I have two group ane is Adminstrator and other is Sales Group in sale group Certain User have to have some roles so I have restric it. If any one have an idea abt how to find roles if we pass only user name only for Particular group in a domain.... Kindly Tell me how to code it in C# so We can restrict users according to thier roles.