The tax extension allows you to delay filing your tax returns until October 15, 2019. This gives you time to collect more documentation or organize receipts.
However, it does not extend the taxes due, so if you think you would owe, you need to make a payment with your extension. You will estimate your taxes based on the information you already have and your previous tax returns.
To prepare and file in TurboTax, all you need to do is click File an Extension in the bottom of the black column on the left. Filing is free.