Your 2018 tax return is not affected by the fact that you did not file your 2017 return.
You can use TurboTax to file your 2017 return but it cannot be done online. There will be a penalty for late filing if you owe taxes for 2017. If you have a refund for 2017, there is no penalty.
Please read this TurboTax on how to prepare your 2017 return:
https://ttlc.intuit.com/replies/3301770
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"