Did you enter direct debit information with your return? That is, did you give the IRS permission to take the tax due directly out of your checking account?
If so, the IRS will take care of the payment; the only thing you need to do is make sure there is money in the account on the date of the direct debit.
If you did not set up direct debit, then you will have several ways to pay what you owe. Please see this IRS webpage on the different ways that you can pay them.
As you already understand, there is no requirement to send the payment with your return - your Social Security number ties your payment to your return.
If you selected “pay by check”, TurboTax will normally recommend that you print a form 1040-V, which is a payment voucher that you would include with your check when you mail it to the IRS. If you print a copy of your return now, or if you save a copy of your return as a PDF, it will probably include form 1040-V. The first page of the PDF will it have instructions for you.
You can also make a direct payment at www.irs.gov/payments, either by direct debit from your banking account so that you don’t have to mail a check, or by credit card (although there is a 3% service charge if you use a credit card).
I filed back in feb. how do i pay my federal tax? i dont remember if i indicated pay by check or direct debit