How do I give my staff a free meal or a discount at the counter without messing up my figures?

Use the Discount button on the selling screen. It takes a percentage or an amount and always asks for a reason, and a manager types their own four numbers to apply it. The reason is stored on the sale, so a month later the discount can still be explained. The Z report shows the total given away in the shift, and the sale keeps the name of the manager who approved it. That means a staff meal is a real sale with a discount on it, not a plate that vanished from the day. The POS and the counter tab in the docs explains discounts and approvals.