Go to Income > Invoices where you can find all invoices for your company.
You can "View", "Download" as PDF, "Add a payment", "Send", or "Duplicate" another invoice in the "Action" menu.
You can also use the filters to find other invoices in a certain period, or with certain number/customer.
The receivable amount will be recorded automatically in your book. Your customer needs to pay this invoice in the near future, after which he/she does, you can proceed to create payments.