You can sell products using the ASAP product module, which is a separate feature that you can add to your standard ASAP package. The product module will allow you to sell products on your online registration website (t-shirts, books, etc.), create product relationship for up-sells, manage shipping or pick-ups, and generate additional income for your organization.
To start using the product module, you need to first speak with your CSM about the cost of this module for your Organisation. Once activated you can start adding products, see this guide for more information- Setting Up Products