You can pay your taxes after you file but any taxes due should be paid by April 15, 2019 to avoid a penalty & interest. If you don't want to pay now when you file, choose to pay your taxes by check, that will get you through to e-file. You can then later send in your payment by check or pay your Federal Taxes due online on the IRS website.
You can pay Federal taxes owed online by credit card or direct debit
If you owe State taxes, you can check your states website, they will have an option to pay online.