Form W4 tells your employer how much tax to withhold from each paycheck. Learn more about how and when to adjust your W-4.The new form has five steps. Employees must fill out step 1 and step 5. In this blog, we'll take you through the ins and outs of the W4 form, shedding light on its significance and how to fill it out correctly. Check your W-4 tax withholding with the IRS Tax Withholding Estimator. See how your withholding affects your refund, paycheck or tax due. You must complete a W-4 form for Payroll Management Services to determine how much income tax to withhold from each paycheck. Information about Form W4, Employee's Withholding Certificate, including recent updates, related forms and instructions on how to file. The w-4 has five steps we'll go through each step briefly then show an example of a young person completing his first w-4.