SQL Insert Query Using C#

I assume you have a connection to your database and you can not do the insert parameters using c #.

You are not adding the parameters in your query. It should look like:

String query = "INSERT INTO dbo.SMS_PW (id,username,password,email) VALUES (@id,@username,@password, @email)";

SqlCommand command = new SqlCommand(query, db.Connection);
command.Parameters.Add("@id","abc");
command.Parameters.Add("@username","abc");
command.Parameters.Add("@password","abc");
command.Parameters.Add("@email","abc");

command.ExecuteNonQuery();

Updated:

using(SqlConnection connection = new SqlConnection(_connectionString))
{
    String query = "INSERT INTO dbo.SMS_PW (id,username,password,email) VALUES (@id,@username,@password, @email)";

    using(SqlCommand command = new SqlCommand(query, connection))
    {
        command.Parameters.AddWithValue("@id", "abc");
        command.Parameters.AddWithValue("@username", "abc");
        command.Parameters.AddWithValue("@password", "abc");
        command.Parameters.AddWithValue("@email", "abc");

        connection.Open();
        int result = command.ExecuteNonQuery();

        // Check Error
        if(result < 0)
            Console.WriteLine("Error inserting data into Database!");
    }
}