For Apple Wallet
On iPhone: Open the wallet app and tap the "+" sign. Fill out your details and you're ready to go.
For Apple Watch: Open the "Wallet & Apple Pay" and select "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 select "Add Card".
For Google Pay:
Download the Archa app from Google Play or the App Store. Then, just follow the instructions in the app. You can also set up GooglePay on the web at pay.google.com.