Write a check and mail it to the IRS in Texas (they changed the address from the former Philadelphia address) - staple it to your 1040 (and keep a copy), and then send via Fed Ex so you can prove you sent it.
To make sure you ha everything correct and can read "governmentese", go to the IRS Website and download PUBLICATION 501 (PDF F0rmqt). That has all the information you will need.
