Read sql data and write an output txt file in vb.net

Hi, support team:

I have a xml-txt already received the data (part2 below), but right now I need to write a new vb.net program use SQLDataReader to read the data from SQL server and StreamWriter output txt file (part1 below), I need a help for the following and correct my part2 syntax.  

1) when to use SqlDataReader.GetString () and SqlDataReader.GetInt32() method to retrieve the field?
2) GetValue() and GetOrdinal() method?
3).ToString() method?    
any help is very appreciated, thanks! (hope I made my question clear)

'part1 - Is this the right code?
***********************************
Dim strRecordType As String = sdr.GetValue(sdr.GetOrdinal("RecordType")).ToString
Dim intDocumentNo As Integer = sdr.GetValue(sdr.GetOrdinal("DocumentNo")).GetInt32

strExpDelim="|"
swOutput.Write("H" _
                        + strExpDelim + intPONum.ToString _
                        + strExpDelim + strOrderDate _
                        + strExpDelim + strRecordType _
                        + strExpDelim + intDocumentNo _
                        + vbCrLf)

'part2 - read the xml convert to txt
*****************************************
     Dim filename As String
     filename = "C:\test.xml"
     Dim m_xmlr As XmlTextReader
     m_xmlr = New XmlTextReader(filename)
     m_xmlr.WhitespaceHandling = WhitespaceHandling.None
 
     While Not m_xmlr.EOF
     m_xmlr.Read()
     If Not m_xmlr.IsStartElement() Then
     Exit While
     End If
     m_xmlr.Read()
     Dim RecordType = m_xmlr.ReadElementString("RecordType")
     Dim DocumentNo = m_xmlr.ReadElementString("DocumentNo")
     Dim OrderDate = m_xmlr.ReadElementString("OrderDate")
     Dim Title = m_xmlr.ReadElementString("Title")
     Dim Currency = m_xmlr.ReadElementString("Currency")

     Dim ExportTxtFile As String = "C:\test.txt"
     Dim File_Stream As New FileStream(ExportTxtFile , FileMode.Append, FileAccess.Write)
     Dim FileWriter As New StreamWriter(File_Stream)
     With FileWriter
     Try
     .BaseStream.Seek(0, SeekOrigin.End)
     .WriteLine(RecordType _
     & "|" & DocumentNo & "|" _
     & OrderDate & "|" & Title & "|" & Currency)
     Catch ex As IOException
     Debug.Assert(False, ex.ToString)
     Finally
     .Close()
     End Try
     End With
     End While
     m_xmlr.Close()