IRS form W-2 is an end-of-year summary that and employer gives to the employees and also sends to the IRS stating the amount of wages paid, as well as the amount of taxes withheld. Essentially the same information that also appears in the year-to-date column on your last paycheck of the year.You need this information to fill out your form 1040 (individual income tax return) and if you file the 1040 by paper mail, a copy of the W-2 form(s) must be attached.When the IRS receives your 1040, they will compare the W-2 that they got from you with the one they got from your employer.Your employer is required to give or mail it to you by the end of January.