You can use IO.File.AppendAllLines, like this:
Dim desktopPath As String =
Environment.GetFolderPath(Environment.SpecialFolder.Desktop)
Dim fileName As String = "times.txt"
Dim fullPath As String = IO.Path.Combine(desktopPath, fileName)
IO.File.AppendAllLines(fullPath, {"Some new line in the file"})
Other ways to get user desktop folder path: