Windows Authentication and add Authorization Roles through database – MVC asp.net

I am new to mvc4 asp .net and confused with the authentication and authorization. Our’s is an internal website that takes username(HttpContext.Current.User.Identity.Name) from windows authentication and check against database if the username exists and what roles the user has. I want to use the global [Authorize] attribute and roles, to give access to controllers. Can anyone help me on how to start with.