Stacking is on by default. A 20% catalog sale plus a 10% coupon gives both. Use Stop other rules or conditions to prevent it.
Percentage coupons without a cap can give large discounts on big orders. Set Max Discount Cap.
Usage limits count paid orders. Uses are counted when orders are placed, and given back if the order is cancelled or refunded.
COD and after-order rewards. Coupons for next time and customer-group upgrades are given after payment, so for cash-on-delivery orders that's when the order is marked paid.
Guests and "Once per customer". A promotion with the Once per customer condition only works for logged-in shoppers; guests can't use it. Use Per Customer Limit instead if guests should get the offer.
Dates use your store's time zone. Set Valid Until to the end of the last day you mean.
Inactive or expired promotions stop applying straight away, including in carts already open.
GST. Discounts reduce the taxable price of the items, so GST is charged on the discounted amount.
Coupons generated for customers (the Generate coupon bonus or Auto Coupons) are single codes; manage them under Auto Coupons.
