need help to understand code

[sylviam]

hello guys i am wondering if any of you could explain what this code do and how it works.

Private Sub Workbook_Open()
    lastSelectionChange = Now
    closeWB
End Sub

Private Sub Workbook_SheetSelectionChange(ByVal Sh As Object, ByVal Target As Range)
    lastSelectionChange = Now
    'MsgBox (Now)
End Sub
Private Sub Workbook_SheetChange(ByVal Sh As Object, ByVal Target As Range)
    lastSelectionChange = Now
    'MsgBox (Now)
End Sub


Module 1 
Public lastSelectionChange As Date


Sub closeWB() // sluit workbook
    If DateDiff("n", lastSelectionChange, Now) > 5 Then
        ThisWorkbook.Close SaveChanges:=True
    Else
        Application.OnTime Now + TimeSerial(0, 1, 0), "closeWb"
    End If
End Sub

I am kinda new and wonder how this works . like what is a function or what value's do they have.

Kind regards