The W-2 statement shows how much you have earned, and how much was taken out in federal taxes. For any year in which an employer paid you as an employee, CNCS will mail you a W-2 statement by January 31 of the next year. You may receive a W-2 from other employers, also. When you file your taxes, you must include a copy of each W-2 statement.
See also:
What do I need to do with the W-2 statement?
Who should I contact if a correction needs to be made on my W-2 statement?