How can I connet weighing scale through RS232 usb cable

Public Class Form1
    Dim SerialPort1 As IO.Ports.SerialPort


    Delegate Sub SetTextCallback(ByVal data As String)

    Private Delegate Sub UpdateLabelDelegate(theText As String)
    Private Sub UpdateLabel(theText As String)
        If Me.InvokeRequired Then
            Me.Invoke(New UpdateLabelDelegate(AddressOf UpdateLabel), theText)
        Else
            TextBox1.Text = theText
        End If
    End Sub

    Private Sub SerialPort1_DataReceived(ByVal sender As System.Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles SerialPort1.DataReceived
        Dim returnStr As String
        returnStr = SerialPort1.ReadExisting
        Me.BeginInvoke(Sub()

                           UpdateLabel(returnStr)
                       End Sub)
    End Sub

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        SerialPort1.Open()

    End Sub

    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
        SerialPort1.Close()
    End Sub
End Class