To use Stripe for Elementor Pro Form, you need a Stripe account obviously to receive the payment. In order to connect it with your form, you'll need API access which you can access from your stripe account.
To create a new API, you need to login and navigate to your Stripe dashboard > Developers > API Keys
Here you can create and get the publishable key and secret key for your stripe which you can, later on, specify in Dynamic Content > APIs > Stripe
Learn more about stripe API documentation here: