Well, homework is usually an assignment given by a teacher to his/her students after class. It is called so because usually it is finished back at home. An assignment is a particular task assigned to someone or a group of persons, and usually it must be done within a certain period of time. So it's similar to a "task". "Duty" sounds more mandatory than simply a job or a task, which means it's something you MUST do. A job is either a particular task or a job position, i.e. being a teacher, an engineer, a manager, etc. I hope this will help you.

they are make me down before i work it, but it also increase our ability for something :)