I need to stop midway through this form and I don't know how to save what I've already entered. Can you show me? There is no "save and return later" option

 TurboTax Online automatically saves your work as you go through the interview.

Plus, when you sign out, we'll make sure to save everything before we log you out.

Once you've filed your return, we'll also give you the option to save a PDF copy of your tax return to your computer so you can view or print it without having to sign in again.

Where in the screen do I sign out?

Do I sign out by pressing red dot on upper left hand corner of screen?

To log out of TurboTax Online, click on Sign Out in the bottom left corner of the screen.  You can also just close your browser window as TurboTax saves your work as you go.   Maximize your screen if you do not see the Sign-Out link.