Ready to mail indicates that the tax return has not been e-filed. You will have to print, sign, date and mail the federal tax return to the IRS.
Or e-file the tax return using the procedure in this TurboTax support FAQ - https://ttlc.intuit.com/community/e-file/help/how-do-i-change-from-mail-to-e-file-in-turbotax-online...
You complete your tax return by finishing all 3 Steps in the File section. In Step 3, to e-file your tax return, you must click on the large Orange button labeled "Transmit my returns now".
After completing the File section and e-filing your tax return you will receive two emails from TurboTax. The first email when your tax return was transmitted and the second email when the tax return has either been accepted or rejected.