Using a Promo URL will allow you to offer discounts to your customers by sending out custom links, or having the links installed on certain web pages. Use of a promo URL will automatically apply the discount to the customer orders, so can be handy if you're running a special or want to have local businesses or partners be able to offer discounted pricing for your event.
Promo URLs are available for every promo code you have on the system. The custom promo URL just adds ?promo_code=CODE (replace "CODE" with your promo code) to the end of an event, venue, or all events page URL. You can add that manually, or when you're on the Manage Codes page you can click the "View Promo URL" button display and copy the custom URL.
When a customer uses that link to go to the venue or event page the discount will be automatically applied to their order total after they add tickets to cart. So, the customer does not need to enter the code (nor can they forget to add it!). Promo URL usage is tracked the same way as regular promo code submissions. So, in your reporting you'll easily be able to track how many tickets have been sold from that link by filtering for the promo code.