This block is used to display payment form on billing form in Admin panel. In
most cases it is enough to use the \Magento\Payment\Block\Form\Cc. All payments details are displayed according to specified keys in paymentInfoKeys option in module configuration.
Example of custom formBlockType: Braintree payment method implementation
In the integration with the Braintree payment provider, we use the \Magento\Braintree\Block\Form class as formBlockType. It allows displaying only card types available for configured countries:
For creating a template for the payment information rendering class, you can use the default cc.phtml as example.
Then add the the template to the billing form layout sales_order_create_index.xml.