...
At the bottom of the form, the Discount fields show the percent of discount applied to the document amount (prices) and the total discount amount calculated on the manual discounts.
The VAT field shows the total VAT amount calculated for the invoice, and the Total Due shows the document total to be paid by the customer.
Note. All the amounts are shown in the document currency.
The Prepayment field shows the amount of advance payments from the customer that is applied to this invoice. For details on applying advance payments, see Offset Prepayments.
...
After filling out the tab, click the Save button to save your work. After filling out all the tabs, click Post to save and post the document without closing it or Post and close to save, post, and close the document.
Use the Settings button to invoke the Document Settings dialog box that can be used to move the Warehouse field or other fields from the document header (the Main tab) as columns to the table on the Inventory and Services tab or back.
The Document Settings dialog box
Use the Generate button to create a document based on this invoice.
...