AutoFill and ‘Payment Request API’ behavior in chrome

According to this guidance in Chrome Help

Chrome has 2 mechanisms that support saving the payment methods for the browser’s user: – Autofill and the Payment Request API
My Questions

  • what are the difference between them from user experience?
  • When using basic card (credit or debit card) what is the card number stored for continues use, is it stored in some chrome data repository where all the passwords to enter websites is stored?