In order to E-file your Tax Returns in TurboTax Online, you need to walk through the "File" section of TurboTax.
Click the "File" tab, which is found on the left side of your screen in black. (Click on Screenshot Square below for reference)
You must walk through the 3 steps and then click the button that says "Transmit My Returns Now".
If you are using TurboTax Download/CD Desktop Software, the "File" Tab is located near the top of your screen.
Once you have completed the "File" process, you can keep track of your return status here: https://turbotax.intuit.com/tax-tools/wheres-my-refund/.
[Edited 4/12/2019 | 5:32PM EST]