Every year, around the 1st of January through April 15th every working American is expected to file an income tax return with the IRS. This return is used by the IRS to determine what your overall tax bill should have been for the previous year. Using a number of forms provided by the IRS everyone has to report their income and expenses.
The agents of the IRS will then review your tax return and determine whether or not all of the information is correct and that you either sent a check to cover what you owe the IRS or whether you are entitled to a refund check. With that said, if it is determined that there are any issues with your tax return, this will trigger the IRS to take a deeper look at your return and more than likely request an audit.