how will data insert through foreign key

protected void Page_Load(object sender, EventArgs e)
    {

       // Label1.Text = Request.QueryString["user"].ToString();
        Label1.Text = "welcome "+Request.QueryString["user"];
         TextBox4.Text = Request.QueryString["id"];//f_k


    }

    protected void Button1_Click(object sender, EventArgs e)
    {
        conn.Open();
        cmd.Connection = conn;
        cmd.CommandText = "insert into book_info values('" + TextBox4.Text + "','" + TextBox1.Text + "','" + TextBox2.Text + "','" + TextBox3.Text + "')";
        cmd.ExecuteNonQuery();
        conn.Close();


        TextBox1.Text = "";
        TextBox2.Text = "";
        TextBox3.Text = "";
    }

}