how to handle An exception of type 'System.Data.SqlClient.SqlException' occurred in System.Data.dll but was not handled in user code

protected void Button1_Click(object sender, EventArgs e)
   {
       SqlConnection conn = new SqlConnection("Data Source=localhost\\SqlExpress;Initial Catalog=dad1;Integrated Security=True");
       string pass = "pppp", rol = "rrrr", sql;

       sql = "SELECT * FROM UserName where Name ='" + TextBox1.Text + "' ";
       SqlCommand comm = new SqlCommand(sql, conn);
       conn.Open();

       SqlDataReader reader = comm.ExecuteReader(); \\ this is problem
       if (reader.Read())
       {
           pass = (string)reader["password"];
           rol = (string)reader["role"];
       }
       else
       { Label1.Text = "no user found "; }
       reader.Close();
       conn.Close();
       if (TextBox2.Text == pass)
       {
           Session["Authencated"] = rol;
           if (rol == "Admin")
               Server.Transfer("Default2.aspx");
           else
               Server.Transfer("Default3.aspx");
       }
       else
           Label1.Text = "wrong password";

   }