There are two tasks here, closely related to each other but distinct — writing the job description, and writing the job advert. Both are written with a view to publishing externally in due course, and will be published as a single item.
Be ready to re-write the job description and advert if necessary: if you publish the job advert on external websites, you may want to consider adapting the advert for the context.
Writing a Job Description
The job description should use aspects of the person profile, especially the required or ideal skills and abilities, but it must describe some important elements that are different from the person profile.
There are two key parts of the job description.