You can file an extension here: https://turbotax.intuit.com/irs-tax-extensions.

Your extension must be filed by the April deadline for filing taxes.

You can also download Form 4868 from the IRS website, print it and fill it out manually, and mail it by April 15. Complete instructions will be on your printout.

Your extension will give you until October 15 to file, but it does not give you additional time to pay any taxes you may owe. These are still due by April 15 (June 15 if you're out of the country).