To expand, it's these 7 lines. (Actually 12)

    <form action="/your-server-side-code" method="POST">
      <script
        src="https://checkout.stripe.com/checkout.js" class="stripe-button"
        data-key="pk_test_6pRNASCoBOKtIshFeQd4XMUh"
        data-amount="999"
        data-name="Stripe.com"
        data-description="Widget"
        data-image="https://stripe.com/img/documentation/checkout/marketplace.png"
        data-locale="auto"
        data-zip-code="true">
      </script>
    </form>

- more or less. Maybe not precisely that, but it's the bit where you add a payment form to your website.

It's a nice headline, but it really leaves out the tremendous amount of back-end work that went into making that front end easy to use.