Go to Account Settings → Account Services and click the “Connect Stripe” button. Follow the prompts to either create or connect a Stripe account.
Once you have connected your Stripe account you will have two payment accounts created, one in “Live” mode and another in "Test" mode. You can use "Test" mode to test your form and submissions with test credit cards.
You can choose which payment account you would like to use on a form by going to Configure → Payments and choosing the appropriate account.
The number of payment accounts you can connect will depend on what plan you are on: