Will I have to enter a PIN or sign a receipt?

It depends on the merchant. In some cases you may need to sign a receipt or enter your PIN. If asked to verify the last four digits of your debit card number when making a purchase, provide the last four digits of the device account number. The device account number can be found by selecting the Settings icon on your compatible Apple device (Apple Watch users launch the Apple Watch app). Then scroll down to Apple Pay™, select the card and scroll down to view the Device Account Number.