I just want to print a copy of my tax returns and mail them to the IRS and the state. How do I do that, and do I still have to pay Turbo Tax if my refund/tax is 0?

If you have not paid for the online edition you are using, have not filed your tax return or registered the Free edition, then you can clear your return and start over with a lower priced edition.  Click on My Account at the top of the program screen while working on the 2017 online tax return.  Click on Clear & Start Over.  You have the option of using TurboTax Free Edition, but I would suggest looking at the difference between the two at https://turbotax.intuit.com/personal-taxes/compare/online/

Doing this will let you know if the free edition will work for your specific tax situation. Hope this helps!