How to fill out a W-4 form By: J.D. The first line on a W-4 is where you put your name. You also put your address. The second line is where you where you put your social security number. Line three is where you put your if you are single or married. The rest of the lines are for if you’re claiming any exemptions, allowances, and withholdings. It is important to write who your employer is.