You purchased the TurboTax desktop CD/Download edition from Costco. You need to download and install the software on your personal computer, not use the TurboTax online editions.
See this TurboTax support FAQ for using the desktop editions and the license code - https://ttlc.intuit.com/turbotax-support/en-us/help-article/license-information/install-turbotax-cd-...
