I am not sure what is your question? What exactly is your problem?
"How do i write an application?" is not a question we can help with (except
may be with the answer "hire a programmer")
Can you make a web form that runs "UPDATE" or "SELECT" statement?
If you can then just replace "UPDATE" with "BACKUP DATABASE" and change your
connection string to connect to master database....
If you can not then you will need to go to
http://asp.net/learn/ and learn
how to make a web form...
George.