you enter the extension payment in your 1040 if it was not automatically entered by Turbotax
https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-extension/filed-extension-made-payme...
once entered you go through the rest of the return. eventually you get to a screen which asks if you want to e-file or mail. if you select mail you will have to print, sign and date and include any withholding forms and mail to the address in the Turbotax filing instructions. if you select e-file you will continue on until you get to a page which says TRANSMIT. click on it to E-file. some additional info may be required. especially if yo have a state return also.
