To complete and file a 2018 tax return using TurboTax you would need to purchase, download and install on a personal computer one of the 2018 desktop editions from this website - https://turbotax.intuit.com/personal-taxes/past-years-products/

A 2018 tax return can only be printed and mailed, it cannot be e-filed.

See this TurboTax support FAQ for the minimum system requirements using Windows - https://ttlc.intuit.com/community/system-requirements/help/minimum-system-requirements-for-turbotax-...

See this TurboTax support FAQ for the minimum system requirements using a Mac - https://ttlc.intuit.com/community/system-requirements/help/minimum-system-requirements-for-turbotax-...