When you provide some goods or services to a customer you normally expect to be paid. Sometimes the customer will pay immediately, in which case you treat the transaction as a Cash Sale — see Entering Receipts. On other occasions you will give the customer an invoice indicating how much is to be paid and he or she will pay at some future date. In this situation you would use the debtors ledger to record the transaction as a Sales Invoice.
Note: In MoneyWorks Gold, if you recorded the sale using a Sales Order and processed it using the Ship command, you do not need to enter the invoice again—the invoice will have been automatically created for you when you shipped the goods — see Shipping Goods.