People will get an automatic extension of 6-months to file their tax returns but not for the paying due amount. Due amount must pay on or before actual Due Date (Apr 15th).

For extension applied people due date would be Oct 15th.

To get extension file Form 4868 either electronically or paper version. Or to get the extension pay all or part of your estimated income tax due and indicate that the payment is for an Extension purpose using Credit, Debit, Direct Pay etc.