Have you ever seen your W-2 before tax filing? One of the things that you can do is to check your W-2 form since there could be some mistakes regarding your income, withholding or other information which will create problems when filing your taxes. Check your W-2 against your pay stubs and make sure that figures match and are reasonable. In case you still have no idea about what W-2 is, consider it as a document which gives information about how much money you made and how many taxes were taken out of your salary.