In order to file for a six-month tax extension, you need to file Form 4868.
The form will ask you for the names of those filing, address, Social Security number, and estimate of moneys owed, payments you have made, remaining amount due and amount being paid.
You have to file the form no later than April 15, 2014, tax day. It’s free to file for the extension and can be done electronically or through the mail. If filing by mail, the parcel must be postmarked on or before April 15.
The extension only gives you more time to file, NOT MORE TIME TO PAY. To avoid all of the nasty penalties and such, you still need to pay (estimated) moneys owed by April 15. You will find all of the different payment methods here.