A W-4 form (officially known as “Form W-4”) is what a full-time employee fills out for their employer when they start a new job. This form tells the employer how many deductions you will take when you file your personal tax return.
If you have ever been an employee, you've likely received a W-2 at the end of the year from your employer. It's not something you fill out. The form shows how much you've earned and how much was deducted for taxes and contributed to retirement plans.