You can use ADO.NET to create database for the website, and then connect to it with the C# application. or you can do someting that call "web service" - open new ASP.NET Web service in your Visual Stduio, there, you can define methods that after you can call to then with your C#. after you finish define, go to the C# project, and then on the solution explorer->referance of the project click left mouse, click "Web referance", and look for your web service address, then you can use all the methods you defined.
Gindi Bar Yahav - Web & Software developer.