Ledger1 doesn't have an invoice built into it, but one might be added in the future if there seems to be a user preference for one.
Ledger1 was designed to export invoice data to external invoicing applications. The way to do this is to attach an invoice number (custom field #8) or an order number (custom field #4) to each transaction that you want to appear on an invoice. To export invoice data to a file, first filter the Ledger on the desired invoice number, then click on the export button. Clicking the export button will create a data file that will contain the invoice data that was filtered. This file can then be imported to your invoicing application. Alternatively, an invoice page could be added as a new page in Ledger1 and formulas could be used to pull the invoice data from the Transaction Table. A third option would be to create an invoice in MS Word, and create a merge using the previously mentioned export file.