You asked: "How do I download tax processing software ?The site looks like it keeps all my data separate from my computer.??"
You didn't mention a tax year, so I'll assume you are asking in regard to preparing a 2020 return.
Are you currently using Online TurboTax (web version?) If so, in that online product one uses a browser to work on the return, and the data is stored online, not locally on your computer. It is the desktop software (CD/download), that one can install on one's computer and not have to use Online TurboTax. In the desktop products the data files are stored locally on one's computer. So are you asking how to purchase a download of the desktop software to install on your computer?
We don't know what you have already done or not. Have you already purchased the desktop software and just need to download it? Or are you asking where to buy it? If you haven't bought it yet and want to buy it directly from TurboTax, here is the page for 2020 tax product:
https://turbotax.intuit.com/personal-taxes/cd-download/
If you need prior-year software (2019, 2018, 2017), here is where to buy
https://turbotax.intuit.com/personal-taxes/past-years-products/
