MS SQL can be used as an ASP.NET backend . You do that by creating a connection string in your app configuration file . the connection string contains information that identifies or has the name for the database you want to connect to . it also contains the username and password neccesary for you to connect to the database .
then create an SqlConnection object in code in your application which takes this connection string as a parameter . open the instance of the sqlconnection object ie SqlConnection.open(). You will now be able to interact with the database