A purpose of a job advertisement is to notify the public about an open job position.
The main goal of a job advertisement is to inform potential job candidates about a new opening and attract them to apply.
A basic structure of job advertisement is shown below in the image.
1) commander and chief of the American government
2) where the applicant is most likely to work.
3) a list of duties/ responsibilities
4) qualifications required. ie education/ experience
5) introduce America its government. Along with it include job benefits.
6) how the applicant can contact you.
Hope this helps!
Good luck