هل يمكن شرح الكود التالي

[الطالب المثابر]

السلام عليكم ورحمة الله وبركاته

اخواني الافاضل هل يمكنك شرح الكود التالي لي بالتفصيل لان بعض النقاط مو واضحه لي

Option Compare Database
Option Explicit

' Code to display standard "Open File" dialog.

Type OPEN_FILENAME
  lStructSize As Long
  hwndOwner As Long
  hInstance As Long
  lpstrFilter As String
  lpstrCustomFilter As String
  nMaxCustFilter As Long
  nFilterIndex As Long
  lpstrFile As String
  nMaxFile As Long
  lpstrFileTitle As String
  nMaxFileTitle As Long
  lpstrInitialDir As String
  lpstrTitle As String
  flags As Long
  nFileOffset As Integer
  nFileExtension As Integer
  lpstrDefExt As String
  lCustData As Long
  lpfnHook As Long
  lpTemplateName As String
End Type

Private Declare Function GetOpenFileName Lib "comdlg32.dll" Alias _
  "GetOpenFileNameA" (OFN As OPEN_FILENAME) As Boolean

Private Declare Function GetSaveFileName Lib "comdlg32.dll" Alias _
  "GetSaveFileNameA" (OFN As OPEN_FILENAME) As Boolean

Private Const ALLFILES = "All files"

Function MakeFilterString(ParamArray varFilt() As Variant) As String
' Create filter string.
' Returns "" if there are no arguments.
' Expects an even number of arguments (filter name, extension).
' Adds *.* if the number of arguments is odd.

  Dim strFilter As String
  Dim intRes As Integer
  Dim intNum As Integer

  intNum = UBound(varFilt)
  If (intNum <> -1) Then
    For intRes = 0 To intNum
      strFilter = strFilter & varFilt(intRes) & vbNullChar
    Next
    If intNum Mod 2 = 0 Then
      strFilter = strFilter & "*.*" & vbNullChar
    End If

    strFilter = strFilter & vbNullChar
  End If

  MakeFilterString = strFilter
End Function

Private Sub InitOFN(OFN As OPEN_FILENAME)
  With OFN
    ' Initialize fields user doesn't want to know about
    .hwndOwner = hWndAccessApp
    .hInstance = 0
    .lpstrCustomFilter = vbNullString
    .nMaxCustFilter = 0
    .lpfnHook = 0
    .lpTemplateName = 0
    .lCustData = 0
    .nMaxFile = 511
    .lpstrFileTitle = String(512, vbNullChar)
    .nMaxFileTitle = 511
    .lStructSize = Len(OFN)
    ' Use default filter if not specified.
    If .lpstrFilter = "" Then
      .lpstrFilter = MakeFilterString(ALLFILES)
    End If
    ' Pad lpstrFile with null chars.
    .lpstrFile = .lpstrFile & String(512 - Len(.lpstrFile), vbNullChar)
  End With
End Sub

Function OpenDialog(OFN As OPEN_FILENAME) As Boolean
  Dim intRes As Integer
  InitOFN OFN
  intRes = GetOpenFileName(OFN)
  If intRes Then
    ' Remove trailing null chars from lpstrFile.
    With OFN
      .lpstrFile = Left$(.lpstrFile, InStr(.lpstrFile, vbNullChar) - 1)
    End With
  End If
  OpenDialog = intRes
End Function