This is only an extension of time to file, not to pay. You still need to pay any tax you expect to owe by the regular due date.
You can use IRS Direct Pay or one of the other electronic payment options found at IRS.gov/payments. If you pay electronically first and mark it as an extension payment, then you don’t need to file a separate Form 4868.
If you can’t pay all that you owe, pay what you can and file anyway. That way, you’ll minimize any penalty and interest charges. Then, look at your payment options, such as applying online for a monthly installment agreement. Special rules mean that some taxpayers don’t even need to ask for an extension. This includes taxpayers abroad, certain members of the military, and taxpayers affected by certain natural disasters.
Make sure you file your return by the extension due date.