If you bought TurboTax Desktop, you need to download the software onto your computer from this link, install it and, as you follow the steps, the application will ask you to activate your product. Here's a link explaining all the steps involved in installing the Desktop version. 
 

For 2nd and 3rd installation, at the step asking for the account info, you have to enter the account information where the code was originally activated.

Thank you for choosing TurboTax.