Each digital wallet is slightly different but all make it easy. To add a card to Apple Pay, on your mobile device open the Apple Wallet and click the + sign and follow the instructions for adding a Credit or Debit card. To add a card to Google Pay, on your mobile device open Google Pay and tap on Profile Picture Bank Accounts and Cards and follow the instructions. In Samsung Pay, on your mobile device, open Samsung Pay and tap Menu in the top left corner. Then tap Cards, Add card and follow the instructions to add a credit/debit card.
In each instance follow all on-screen instructions to completion.