I've simplified it and added some comments. Is this any better?
Private Sub Worksheet_SelectionChange(ByVal Target As Range)
If Not Intersect(Target, Me.Range("$C$2:$M$3")) Is Nothing Then
Application.StatusBar = "Created by: ..."
Else
sr = Target.Row
sc = Target.Column
Inquiry = Me.Cells(sr, sc)
If Not Intersect(Target, Me.Range("B9:B28,E9:F28,I9:L28")) Is Nothing Then
MyDesc1 = Application.VLookup(Inquiry, [PN_STATUS], 2, 0)
MyDesc2 = Application.VLookup(Inquiry, [SUPPLY_TYPE], 2, 0)
MyDesc3 = Application.VLookup(Inquiry, [UOM], 2, 0)
MyDesc4 = Application.VLookup(Inquiry, [MAKE_BUY], 2, 0)
Application.StatusBar = Inquiry & " - " & MyDesc1 & MyDesc2 & MyDesc3 & MyDesc4
ElseIf Not Intersect(Target, Me.Range("E9:F28")) Is Nothing Then
'<<<<<<<<<<< You can't test multi-cells, need another approach
'If IsEmpty(Range("$E$9:$F$28").Value) = False Then
If Application.CountIf(Me.Range("$E$9:$F$28"), "<>") > 0 Then
MyDesc5 = Application.VLookup(Inquiry, [OIB], 8, 0)
Application.StatusBar = Inquiry & ": Quantity On-Hand=" & MyDesc5
End If
ElseIf Not Intersect(Target, Me.Range("D9:D28")) Is Nothing Then
If Me.Range("D9:D28").Value = [PP] Then '<<<<<<<<<<<<<<<< is this [PP] or if PP where is that defined
Application.StatusBar = Inquiry & ": New Piece Part Setup needs to take place for this Part Number."
End If
End If
End If
End Sub