What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
Unfortunately, the form does not have a function that add products in a cart. You can add a payment integration and it will directly process the payment after the submit button is clicked.
However, if you have an ecommerce website with your own payment integration, then perhaps you can pass the submission data using POST method on your "Add to Cart" system or script. Here's a guide about it: https://www.jotform.com/help/213-Send-POST-Data-From-JotForm-Using-PHP-in-Custom-Thank-You-Page
May we know what kind of platform you are using? Perhaps we can check it further.
I am using bigcommerce
The payment tool on the form itself acts as a shopping cart and the payments are processed directly from the form itself. It may be possible to send the products selected on the form to bigcommerce using its API or webhooks, but it seems that it is required to have a good knowledge in using bigcommerce API. You may need to hire a developer to achieve this requirement.
Hope this information helps!