The setup is easy as pie:
On your iPhone, open the Wallet app and tap the “+” sign to add a card.
For Apple Watch, open the Apple Watch app on your iPhone and select “Wallet & Apple Pay”, then tap on “Add Credit or Debit Card.”
On iPad, go to Settings, open “Wallet & Apple Pay” and select “Add Credit or Debit Card.”
On MacBook Pro with Touch ID, go to System Preferences, select “Wallet & Apple Pay”, then tap the “+” sign to add a card.