vb.net如何操作xml的element和node?

Public Function WriteConfigInfo(ByVal aSection As String, ByVal aKey As String, _
ByVal aValue As String, ByVal aFileName As String) As Boolean

If aSection = "" Then Return False
If aFileName = "" Then Return (False)
' create in instance of the class and write the config file info
Dim XmlFile As New clsXMLCfgFile(aFileName)
Return XmlFile.WriteConfigInfo(aSection, aKey, aValue)

End Function
Public Class clsXMLCfgFile

Dim Doc As New XmlDocument()
Dim FileName As String
Dim doesExist As Boolean