How can I file 2016 and 2017 before 2018 on here?

[VolvoGirl]

You can't.  Online is only good for 2018 now.

You can only buy the download for prior years.  You have to buy a separate program for each year.  They only sell the last 3 years.  You need a full Windows or Mac computer to install it on.  Buy the download here   

  https://turbotax.intuit.com/personal-taxes/past-years-products/

You have to print and mail prior year returns.  When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s.  Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS received the return.  Don’t forget state.

Important!  Mail Federal and State in separate envelopes and mail each year in separate envelopes.

[BMcCalpin]

One addition to VolvoGirl's excellent answer: don't delay filing the 2018 just because you haven't done the 2016 or 2017 yet. Each year's tax filing processing is largely independent. If you have the data ready to do the 2018 return, then do it, and then work on gathering the other tax information. That is, there is no requirement (once they are late) to do the returns in chronological order. Do whatever you can as soon as you can (because this cuts off interest and sometimes penalties if you owe the IRS).

[VolvoGirl]

Well if you can do them in order you will be able to transfer each one into the next year.  Online will be open until Oct 15, 2019 to do 2018.  You can transfer from 2017 on your computer into 2018 online.