I want to add a payment method

You can use one of our payment processors in order to add a payment method in your form.

You can just drag them into the work space. After dragging them in the work space, the payment wizard will appear where you can integrate your credentials, API, add products and options.

Helpful guides:
Order-Form-Types
Setting-Up-Your-First-Order-Form
How-to-setup-a-recurring-payment-option
PayPal-Forms

You can also check the Payments section in the User Guide.