Here is my setup:
My sprints contain stories, most of which are parts of larger epics. These stories are laid out with user stories, acceptance criteria and other standard info so everyone has full understand of who what when where and why.
Within the stories there are subtasks. some are for frontend team and some are for backend. I have the product managers spec out the stories so they are ready for developers to create these subtasks - what needs to be done to satisfy the story.