You can easily create and schedule discount codes in your store management area. All discount codes apply to the whole cart excluding the shipping costs.
In your store management area, go to Discounts and click Add discount
Create the discount code
(Optional) Specify the discount name; this one is for your personal use – clients won't see your discount name
Specify the discount amount in percent
(Optional) Set up discount conditions:
The total number of uses, i.e., how many times the discount code can be used in your e-store in general
The minimum order amount
(Optional) Specify the period of time during which the coupon is active
You'll see all your discount codes (expired, active, and scheduled) in the Discounts section of your store management area:
You can also set sale prices for each of your products individually.