log in system

I am learning 3-tier architecuture in ASP.NET, C#. I want a login system using this. as i am not so much familiar with this architecture, I am unable to do this. 
I know it is a trivial task for experience guys. Please can any one provide me some examples of doing login system using 3-tier architecuture.
My task is:
--> login system
              check for user validation(username, password) then
                           if user == admin
                                  response redirect to admin.aspx page
                           if user == any other users
                        &nbs ...