From your analysis of the job you can write a job description which will state what the job holder is responsible for and what they are required to do.
There is no one right way of setting out job descriptions. An accurate job description has various uses outside the recruitment process:
For example, it can be used to review staff performance in appraisals or to assess training needs when someone new starts with the organisation.
Within the recruitment process, the job description leads on to the next stage of specifying the type of person you are looking for to fill your vacancy.