It sounds like you might be confusing our CD/download editions and our online editions.
Prepayment codes are typically for our online editions. You'll need to sign in to TurboTax online and prepare your return. When you're done ready to file, you'll enter your code to "pay". Here's more about that: https://turbotax.community.intuit.ca/replies/2648021
If you purchased our download edition, you were issued an IKC on your receipt. When you install TurboTax on your computer, TurboTax will prompt you to enter the IKC from your receipt before you can run TurboTax for the first time. Here's what to do after you've downloaded TurboTax: https://turbotax.community.intuit.ca/replies/3169457
