A job description is an internal document that describes the general tasks, or other related duties, and responsibilities of a position. It should specify the functionary to whom the position reports, specifications such as the qualifications or skills needed by the person in the job, and a salary range.
Job evaluation is a systematic way of determining the value/worth of a job in relation to other jobs in an organization. It makes a systematic comparison between jobs to assess their relative worth for the purpose of establishing a rational pay structure.
Internal factors include equity, the structure of the specific department or, similar jobs elsewhere in the Industry, and the knowledge, skills, and expertise required.