You will need to fill one out. Have all of the financial information needed to fill out the form, and they'll tell you what to put down as an employee number. The form is used by the employer to determine at what rate you get taxed. If you have a bunch of income and will be making more than the basic personal exemption, they'll tax your earnings at a slightly higher rate so that you don't end up owing money at the end of the year. Just make sure you have a form with you and the pay people will be able to fill in the blanks on any questions you have.