How Join The Payment Section at Jotform

Do you mean to say that you want to add a payment field into your form?

If yes, on your Form Builder page, click on Add Form Element:

After that go to the Payments tab and add the required payment field into the form:

Here is a useful guide: https://www.jotform.com/help/165-setting-up-your-first-order-form

If you are referring to something else, please let us know.