How do I add an sales item

I presume you would like to setup an order form to sell items? 

If so, you need to add a payment tool in your form to sell or accept payments from your customers. Here's a guide that you can follow on how to setup an order form: https://www.jotform.com/help/165-Setting-Up-Your-First-Order-Form 

For the list of payment integrations that we support, you can check this link: https://www.jotform.com/help/323-Mastering-Payment-Form-Integrations-with-JotForm 

Let us know if you need more help on this.