Display Msgbox When Item Selected From Combo Box

Im using code from website: http://www.contextures.com/xlDataVal11.html

to display a combobox when I double click any cell that contains a validation list in it. I'm not great with VBA so I am having problems finding what each part of the code does. This is causing problems for another bit of code that I use to display a msgbox when certain values are selected from the list.

The MsgBox shows up great when I select an item from the validation list but does not work at all when I select the same item from the double-clicked combo box. It would be great if I could get the MsgBox to work both ways. This is the code that displays the MsgBox when target value is selected from list

Private Sub Worksheet_Change(ByVal Target As Range)
Select Case Target.AddressLocal(False, False)
Case Is = "B4", "B5", "B6", "B7", "B8", "B9", "B10", "B11", "B12"
If Target.Value = "H" Then
MsgBox "This is a pop for extra information. Savvy?", vbYesNo, "Yo!"
End If
End Select
End Sub...............