If you choose to use TurboTax for the 2017 tax return you will need to purchase, download and install on a personal computer one of the 2017 desktop editions from this website - https://turbotax.intuit.com/personal-taxes/past-years-products/
A 2017 tax return can only be printed and mailed, it cannot be e-filed.
For tax year 2018 you can use either the TurboTax online or desktop editions. A 2018 tax return can be e-filed using TurboTax at any time up through October 15, 2019. After that date the 2018 tax return can only be printed and mailed.
Go to this website for the online editions - https://turbotax.intuit.com/personal-taxes/online/
Go to this website for the desktop CD/Download editions - https://turbotax.intuit.com/personal-taxes/cd-download/