How to create Login page

SqlConnection con;
    SqlCommand cmd;
    SqlDataReader dr;
    int flag = 0;
    string s1, s2, uname, upass;

write code on btton click event it shoud be great helpful

 con = new SqlConnection("Data Source=.; Initial Catalog=krishna; Integrated Security =true;");
            con.Open();
            cmd = new SqlCommand("select *from register", con);
            dr = cmd.ExecuteReader();
            while (dr.Read())
            {
                uname = dr[2].ToString();
                upass = dr[3].ToString();

                //if (s1.Equals(uname) && (s2.Equals(upass)))
                if (s1 == uname && s2 == upass)
                {
                    flag = 1;
                    break;

                }

            }
            if (flag == 1)
            {
                Server.Transfer("Welcometest.aspx?uname=+"+s1+""); 
                //Response.Redirect("WelcomeStudent.aspx");

            }
            else
            {
                Label3.Visible = true;
            }