The IRS W-4 is a form you fill out when you get a new job. It will be supplied to you by your employer when you start your job. You fill it out then submit it to your new boss or human resources coordinator and they will use the information to correctly withhold taxes from your salary.
The more allowances you have, the less money will be withheld from your paycheck by your employer. It means you will pay less taxes up front. Keep in mind that if you do your taxes for the year and find out not enough was withheld, you’ll owe taxes. Likewise, if too much was withheld then you’ll get a refund.
The IRS W-4 form basically consists of a few lines on a worksheet that help you total up the number of personal allowances you have for tax purposes. Everybody has at least one allowance if they are not claimed as a dependent on their parents’ taxes. If your parents claim you as a dependent, however, you can’t claim the allowance on the first line of the IRS W-4. That’s line A on the worksheet.
Line B asks about your marital status and how many jobs you have. If you are single and have only one job then you enter another allowance to the total.
The rest of the W-4 worksheet is mainly for child and spouse credits.