Discounts can be added to POS orders by either a flat rate or a percentage.
To add a discount to an order in progress, scroll down in the Take Order page to the subtotal.
Click the Add Discount button. This will open a text field and a dropdown menu where you can type in the amount of the discount and the way the discount will be applied (by amount or percentage).
As in the gif below, you can see the results and the final price in the grand total field. Note that the discount added here will apply to the entire order.
To create a standing discount for a given customer, use these instructions.
To set up coupon codes to apply to website orders, use these instructions.