What is permission? What is a role? What are users?

What is a user ? For example, I'm Chen yegui What is a character ？ For example, the identity of system administrator . What are permissions ？ Deleting a log is a log management permission , Adding a user is a user management permission Such as can be The relationship between them is ： The system administrator has log management permission to delete logs , role = jurisdiction Finally, the system administrator assigns a value to chenyegui , user = role