Ben Franklin said the only two certainties in life are death and taxes. Certain to happen, sure, but when? Death row inmates aside, we don't know when we'll die. But the day our income taxes are due is known. Normally it's April 15. That's a Saturday this year, so the government has set Tuesday April 18 as the deadline to file income tax returns.
You have to file income taxes with the federal government every year unless you meet the requirements to be exempt. If you owe money to the IRS and don't pay, they will charge you interest and even pursue criminal charges. Just ask Wesley Snipes, he went to prison for two and a half years over tax issues.