Online payment methods are preferred. The IRS mail is backed up due to COVID-19. Additionally, online payments will give you a receipt that you can show the IRS if they should "lose" your payment.

Paying Your Taxes

Certified mail

If you mail anything to the IRS, send it by certified mail with return receipt so you have proof that your payment was received. You can also stop by your local IRS office and make a noncash payment in person  without an appointment.

Don't forget your state

If you live in a state with an income tax, you may wish to may state estimated tax payments. TurboTax has links to all state tax websites at How do I track my state refund?

Since you cannot set up an account on the IRS site due to lack of prior filings then you can use a third party directly if you wish ... this is the same party you would use on the IRS site anyway and you get the same receipt.  However,  be aware that there is a cost involved when using a CC where as mailing a check is free.  

Also ... FYI ... an estimate is not required since you have never filed in the past then you are exempt from any penalties on the return although you will still owe the taxes.  This is known as the safe harbor rule.