Epic : An epic is usually a large story that is difficult to accomplish in a single sprint. An epic is usually accomplished over the course of months. Epics are usually very broad in scope, lack details, and must be broken into smaller user stories before the story can be developed. Epic is often viewed as being the pinnacle of the work hierarchy. In cases where multiple epics share a common goal, they can be grouped into a still-broader business objective, called a theme.
User Story: Basically, a User Story is a list of what needs to be done within a project. It's similar to a to-do list and is owned by the Scrum Product Owner. It provides the Scrum team with enough to get a sense of what the finished product should be like and to calculate an estimate for completion.
Tasks : Each epic is followed by a set of user stories, and for these stories to become workable components, the Scrum team needs to identify and sort tasks. Depending on the complexity of the task, it can take a few hours to several hours (typically up to 12 hours). The task will be assigned to team members with the relevant skills and expertise. A story can only be considered complete when all tasks associated with it have been completed.
