The cashier program: the screen where the seller rings up an order, totals it with tax, takes payment and prints the receipt.
POS stands for point of sale, the place and moment a sale happens. A POS program shows the items, adds them to the order with a tap or a barcode scan, calculates the total, tax and discount, records how the customer paid and prints the receipt. At the end of the day it gives you a sales report and a till closing.
It is the heart of any shop or restaurant, and when it stops, selling stops, so it should ideally work offline and be quick from the keyboard. In Fanann you start from the restaurant cashier template, adjust it by describing your menu and the way you work, then install it on a Windows PC. Printing goes through the printers installed in Windows, so test your printer before relying on it. Practical tip: receipts show VAT, but check your country's e-invoicing requirements with the official source or your accountant before relying on any program.