when you run asp.net application project from visual
studio,visual studio uses their development server.
It's not the right way to develop asp.net appication.

It's a good idea to use a class say gateway where all
database access codes will be written.in this gateway class
you will implement db connection as follows -

first create another class -

master pages creates a common look in your application.
if we think about the header and footer in our pages,we
create these header and footer in every aspx pages.this
method has disadvantages.if there were any custom page
which dynamically adds header and footer then would be
good.

in some way these codes will help you very much if you need
to know file extension.
method below returns true if extension are any of the following -