Discounts work as new discounted prices you can add to your Event and which are added to a basket as a separate price to your standard tickets.
You can create them as Discount codes first, with specific visibility and Coupons and then add them as a new price to the Price Table on your Event.
Then at checkout, the discounted price can be added to the basket with or without Coupon entry, depending on how you set up the Discount.