Our suggestion is that a pragmatic user story should contain the following elements:

Core user story including actor e.g. as an admin user, I can X so that
Essential functional details – a summary of the core functional details. Bullet points keep this brief and easy to understand
Scenarios – information about what to do in different scenarios. These can be discussed during scoping / sizing sessions and don’t need to be completely exhaustive! Smart engineers will think through scenarios and work with you and the team as they’re building it and agree pragmatic solutions on the fly
Link to designs – ideally these designs should be as fleshed out as possible, but you’ll inevitably need to tweak and iterate the designs as you build
Link to epic or labels – provide wider context on where this story fits into the bigger picture.
Comments or questions – use the comments space to document important decisions or clarify questions. There may be a time lag between agreeing the size and scope of a functional requirement and actually implementing it. Comments that are easy to reference and understand will be super helpful for your future self to re-read and understand why a decision was made.

The simplest way to use an epic is to create an epic which represents a specific feature.