Epics are user-centric groupings of what a user does. They are typically the way we first think of the users’ functional needs; our job is to describe detail.
Features are system-centric groupings of what a system does. They are useful when having release planning discussions to keep conversations at an appropriate level of detail.
User stories are short stories about people who use the product. They contain a name, a brief narrative, acceptance criteria, and conditions for the story to be complete. User stories focus on exactly what the user needs without going into the details on how to achieve it.
A description of a user story should include a name, a brief narrative, acceptance criteria, and conditions for completion.
Tasks are the technical work that a development team performs in order to complete a product backlog item (PBI). Most tasks are defined to be small, and represent no more than a few hours to a day or so of work.