You don't. You login to your Bank of America account, navigate to the rewards area, and click a Flights link. It launches the booking engine. It happens to be outsourced to Orbitz, but it is not marketed or branded as Orbitz. It's no different than booking travel through American Express, Chase or Citi. They all have sites where points can be redeemed for travel, and they are all outsourced to someone. The availability and pricing are not necessarily identical to the operator's own branded site.