firstly you add the namspace....

private void button1_Click(object sender, EventArgs e)

        {

            SqlConnection con = new SqlConnection();

            con.ConnectionString = "Data Source=SR; Initial catalog=nadeem;  user id=sa; password=<123>";

            con.Open();

            SqlCommand cmd = new SqlCommand("insert into login values ('" + textBox1.Text + "',' " + textBox2.Text + " ')", con);

            SqlDataReader dr = cmd.ExecuteReader();

            MessageBox.Show("save your data");

            con.Close();

        }

Regards-Nadeem.