Job is a basic term that describes a set of duties and responsibilities performed by one person or multiple people.
Position is a job held by one person.
Responsibilities are major areas of accountability and are the primary functions of a job.
Duties are functions that the jobholder performs to meet the job's responsibilities. For example, a recruiter has the responsibility to recruit job candidates; the recruiter performs the duty of interviewing to find qualified job candidates.
Tasks are specific activities that jobholders perform to accomplish larger duties and responsibilities. For example, a jobholder might perform the task of inputting general ledger entries into the accounting system as part of the larger responsibility of maintaining the organization's financial accounting system.