Pay Electronically
You don’t need to file Form 4868 if you make a payment using our
electronic payment options. The IRS will automatically process an
extension of time to file when you pay part or all of your estimated
income tax electronically. You can pay online or by phone. See
Making Payments Electronically, later.
this is a copy of 4868 instructions. Is this correct?
Correct. When you pay online and mark the payment as "extension", it also automatically applies the extension to your account.
Nice. So no need to send in any documents. Just finish my taxes by the extension date given correct? Will there be any fees or penalties due?
It depends. If your payment with extension plus any withholding and credits on your tax return cover your tax liability then there will not be any further payments due nor any penalties/interest due. If, however, you still have a tax liability after all payments were applied by 15 Apr then interest and penalties for failure to pay will have accrued since 15 Apr and will be due with your filing.
Finally, if after all payments by 15 Apr are applied and if they exceed your tax liability, the overpayment will be refunded.