A W-2 form is required to be sent by your employer by January 31 and is necessary for filing your taxes. The form reports your wage and salary information, the amount of federal and state taxes withheld, the amount you contributed to your retirement plan, and the amount your employer paid for your healthcare during the previous year among other listings. Upon receiving your W-2, It is important to verify your name and social security number. If it is inaccurate, alert your employer right away. The IRS will also receive a copy of your W-2 and is aware of the taxes you owe or are owed by the IRS. When filing your taxes, attach your W-2 form.