I assume that you would like to create an archive or register of all invoices created and sent out.
As I don't know the set out of your work book, I've made some assumptions and think that the following code may work for you:-
Dim WS1 As Worksheet
Dim WS2 As Worksheet
Set WS1 = Worksheets("Invoices")
Set WS2 = Worksheets("Log")
Application.ScreenUpdating = False
NextRow = WS2.Cells(Rows.Count, 1).End(xlUp).Row + 1
WS2.Cells(NextRow, 1).Resize(1, 3).Value = Array(WS1.Range("L10"), WS1.Range("C10"), WS1.Range("L9"))
Application.ScreenUpdating = True
As I don't know in which cells the required data resides, in lines 12 and 13 of the above code, I've made up some cell references: L10 may be the invoice number, C10 may be the date and L9 may be the invoice value. You'll need to change these cell references to suit yourself.
(Do you perhaps also need to add the Customer name to the "Log" sheet?)
I've also assumed that the sheet names may be "Invoices" as the source sheet and "Log" as the destination sheet. Again change these to suit yourself. The above code also assumes that, in the "Log" sheet, Column A is for the Invoice number, Column B is for the date and Column C is for the value.
You can add the above code to the same module as your first code but call this code from your first one simply by placing the name of this code (SendToLog) just above End Sub in your first code.
If this is a little confusing for you, then please upload a sample of your work book to a free file sharing site such as DropBox, ge.tt or SpeedyShare then post the link to your file back here. We can then have a proper look at your query.
I hope that this helps,