What you buy at Costco is a CD that you install on your own computer. If you don't have a CD drive, you can download an installer by calling the number provided in the box. Turbotax online (the web site) is a completely different program and is priced differently -- they don't crossover to each other.
After installing the program, you can download your tax data file to your computer, open it in Turbotax on your computer, and finish your return.
Or if you want to use the web site, you will need to pay online, then return the CD to Costco for a refund if they will give it.
