The Substack special offers tool is a setting which allows newsletter creators to offer special promotions and discounts to their newsletter. These promotions can be broad (i.e. 10% discount for the month of June for anyone who signs up) or they can be quite targeted (i.e. 20% discount for subscribers who clicked on a specific link and/or a 15% discount for students or users with an academic email). If used correctly, the Substack special offers tool is one of the most valuable tools offered by Substack.
The Substack special offers tool can be accessed under your newsletter “settings” and under the “Special Offers” subsection: