A promo code is a unique code that buyers enter at checkout to receive a discount. Each promo code is scoped to your store and can be set with specific date ranges.
When a buyer has items in their cart that match an active deal, the discount is automatically applied. If a promo code is required, the buyer enters it in the checkout form.
Go to Deals in your dashboard to see all your deals, their status (Active, Scheduled, Expired, Inactive), and redemption counts.