请高手帮忙详解下这个VB代码（请按步解释越详细越好不胜感谢必厚报）

Question

Dim answer As String
On Error GoTo cmdmodify
If Command2.Caption = "修改记录" Then
answer = MsgBox("确定要修改吗？", vbYesNo, "")
If answer = vbYes Then
Command2.Caption = "确定"
Command1.Enabled = False
Command3.Enabled = False
DataGrid1.AllowUpdate = True
Else
Exit Sub
End If
Else
If Not IsNull(DataGrid1.Bookmark) Then
rs_client.Update
End If
Command2.Caption = "修改记录"
Command1.Enabled = True
Command3.Enabled = True
DataGrid1.AllowUpdate = False
MsgBox "修改成功！", vbOKOnly + vbExclamation, ""
End If
cmdmodify:
If Err.Number <> 0 Then
MsgBox Err.Description
End If

Answer 1

Dim answer As String 宣告answer为字符串变数
On Error GoTo cmdmodify 若程式发生错误时执行cmdmodify以下叙述
If Command2.Caption = "修改记录" Then 若Command2.Caption等于"修改记录"
answer = MsgBox("确定要修改吗？", vbYesNo, "") 显示提示并代入answer变数
If answer = vbYes Then 若answer等于vbYes（按下提示中Yes按钮)
Command2.Caption = "确定" 设定Command2.caption为"确定"
Command1.Enabled = False 设定按钮无效
Command3.Enabled = False 设定按钮无效
DataGrid1.AllowUpdate = True 允许DataGrid1更新资料
Else 否则
Exit Sub 退出副程式
End If 结束If判断
Else 否则
If Not IsNull(DataGrid1.Bookmark) Then 若DataGrid1.Bookmark不等于空
rs_client.Update 更新
End If 结束If判断
Command2.Caption = "修改记录" 设定显示在按钮上面文字为"修改记录"
Command1.Enabled = True 设定按钮无效
Command3.Enabled = True 设定按钮无效
DataGrid1.AllowUpdate = False 不允许DataGrid1更新资料
MsgBox "修改成功！", vbOKOnly + vbExclamation, "" 显示提示
End If 结束If判断
cmdmodify:
If Err.Number <> 0 Then 若错误的编号不等于0
MsgBox Err.Description 显示程式错误提示/叙述
End If 结束If判断