I'm afraid you will need to be a bit more specific with your question.
As a general pointer though if you create a table in a worksheet with the data for your invoicing you will be able to build up a database of invoices as you raise them. You could then use this database as a source for an Invoice template and for reporting of sales by customer and month etc.
As a general rule though you are always best putting this sort of information into an accounting package on the basis that missing one invoice could prove very costly.
That said you may find this series of posts useful:
