They really need to do a better job of explaining everything, but especially this. In life, this form is filled out and a submitted to your employer when you start a new job. Nobody other than your employer should ever receive this form for anything (just a good life lesson for everyone^).
The only reason the NHSC has you fill this out is because, for tax purposes (the stipend they give you is taxable income), the NHSC is considered your employer. It doesn’t matter what other jobs you have or have had in the past or whether or not you are working currently or not. They are your employer. You fill out steps 1-5 where applicable, sign it as the employee, and submit it. They fill in their own information where it asks for employer information, because again, they are your employer.