A more thorough explanation:

A W-4 form is a document used by employees to indicate the number of personal exemptions they are claiming for federal income tax purposes. This form is then used by the employer to determine the amount of income to be withheld from the employee's paycheck for tax purposes.

For example, if an employee claims two personal exemptions on their W-4 form, their employer will withhold less money from their paycheck for federal income taxes than if they had claimed zero exemptions.

The W-4 form is important because it helps ensure that employees have enough money withheld from their paychecks to cover their tax liability. If an employee does not have enough money withheld, they may owe additional taxes when they file their tax return.