The W-2 form is a document that employers must furnish to their employee(s) by the February 2nd, 2015 for the 2014 tax year. The deadline is generally January 31st, but this year it fell on a Saturday. The IRS and the State will also receive a copy of the form. Furthermore, the taxing authorities will match the information on this W-2 form with the information provided on your tax return. If there are any mismatches, depending on the error, it can automatically trigger an initial rejection of your tax return or a correspondence audit.
As a working individual, you earn income is subject to federal, state, city and payroll taxes (social security & medicare). The amount of income taxes (not payroll) that are withheld throughout the year depends on the information detailed on the federal form W-4 and state form (NYS uses form IT-2104, each state has a different form) that you completed when you commenced work for your employer. Please note that the more exemptions you claim, the less tax withheld for federal and state income tax purposes.