You need different tax programs for each year. To file last year's taxes, you will have to buy and download the program and install it on your computer. Here is where to buy it: https://turbotax.intuit.com/personal-taxes/past-years-products/
Prior year returns must be printed, signed and mailed. You can no longer efile them.
For 2018, you can use the online products or you can buy and download the CD/download product and install it on your computer. You can find them on the TurboTax web site under Products and Pricing: https://turbotax.intuit.com/ 2018 returns can be efiled or printed and mailed. If you decide to print and mail 2018, don't include it with your 2017 return. Mail each of them in separate envelopes.
You should do your 2017 tax return first so that you can transfer 2017 into 2018 before you start 2018.
