This is connection string to your local database in visual studio
<add name="MySqlConnection" providerName="System.Data.SqlClient" connectionString="data source=.\SQLEXPRESS;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|aspnetdb.mdf;User Instance=true" />
Note that this .mdf file does not have a database inside. It is simply data inside the mdf file. Copy the above connection as it is in web.config file.