First Declare a form level Dataset

Public Class frmCSV
    Dim ds As New DataSet

Next connect to your data source and build your dataset. In this case I am going to build one on the fly with this

Private Sub BuildDS()
     Dim dt As New DataTable
     Dim dr As DataRow
     Dim idColumn As DataColumn = _
         New DataColumn("ID", Type.GetType("System.Int32"))
     Dim FNColumn As DataColumn = _
         New DataColumn("FirstName", Type.GetType("System.String"))
     Dim LNColumn As DataColumn = _
         New DataColumn("LastName", Type.GetType("System.String"))

     dt.Columns.Add(idColumn)
     dt.Columns.Add(FNColumn)
     dt.Columns.Add(LNColumn)

     dr = dt.NewRow()
     dr("ID") = 1
     dr("FirstName") = "Randy"
     dr("LastName") = "Flag"
     dt.Rows.Add(dr)

     dr = dt.NewRow()
     dr("ID") = 2
     dr("FirstName") = "Tom"
     dr("LastName") = "Servo"
     dt.Rows.Add(dr)

     ds.Tables.Add(dt)

 End Sub

Now the code to loop trough your dataset and write the results to a file.

Private Sub WriteDS2CSV(ByVal ds As DataSet, ByVal FilePath As String)
    Dim str As New System.Text.StringBuilder
    For Each dr As DataRow In ds.Tables(0).Rows
        For Each field As Object In dr.ItemArray
            str.Append(field.ToString & ",")
        Next
        str.Replace(",", vbNewLine, str.Length - 1, 1)
    Next
    Try
        My.Computer.FileSystem.WriteAllText(FilePath, str.ToString, False)
        MessageBox.Show("File Created", "Success", MessageBoxButtons.OK)
    Catch ex As Exception
        MessageBox.Show(ex.Message, "Write Error", MessageBoxButtons.OK)
    End Try
End Sub

All that is left is to actually build the dataset and then pass it as well as the file name and path to the WriteDS2CSV sub.

Private Sub btnWriteCSV_Click( _
    ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles btnWriteCSV.Click

    BuildDS()
    WriteDS2CSV(ds, "C:\dsExport.csv")

End Sub

A handy little function to remove the name part of an email address.

Public Class Form1
    Public Function getNameFromEmail(ByVal strEmail As String) As String
        ' This purpose of this function is to return the
        ' name part of an email address. For instance
        ' joe@somewhere.com would return just joe.

        ' Use the IndexOf to find out how many characters
        ' in the @ sign is so I can use that number later
        ' to determine the amount of characters to select
        ' in the substring. 

        Dim i As Integer = strEmail.IndexOf("@")
        Dim newstring As String = strEmail.Substring(0, i)
        Return newstring
    End Function

    Private Sub Button1_Click( _
        ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles Button1.Click

        Dim emailArray() As String = { _
            "me@somewhere.com", _
            "you@anywhere.com", _
            "them@nowhere.com"}

        For Each emailName As String In emailArray
            Dim strMess As String = CStr(getNameFromEmail(emailName))
            MessageBox.Show(strMess, "Email Name Test", _
            MessageBoxButtons.OK)
        Next
    End Sub
End Class