The easiest way to activate a new card at point of sale is to scan it. It is not necessary to select any buttons before scanning the card. Note that the prefix numbers in the card indicate whether it is a Reward Card or Tender Card. If you have not specified prefixes in System Options for reward cards vs. tender cards, then a prompt to indicate what type of card you want to activate.
After you make your selection (or immediately after scanning, if you have specified prefixes), a Reward Card or Tender Card line will be added to the sale.