Can you tell me where to start for a 1040 ES filing?

Do you want to prepare 1040ES Estimates?  I don't think the Free Edition has the Estimates.

To prepare estimates for next year you start with your current return, but be careful not to change anything.  If you can't get back into your return, Click on Add a State to let you back into your retun.

You can just type W4 in the search box at the top of your return , click on Find. Then Click on Jump To and it will take you to the estimated tax payments section. Say no to changing your W-4 and the next screen will start the estimated taxes section.

Or Go to….
Federal Taxes or Personal (Deskop H&B)
Other Tax Situations
Other Tax Forms
Form W-4 and Estimated Taxes - Click the Start or Update button