An epic is a larger goal that several issues belong to. "Rebuild the checkout" is an epic; the eleven issues underneath it are the work.
Why they earn their place
Without epics a board is a flat list, and a flat list answers "what is everyone doing" but never "are we actually getting anywhere". Epics are what let you group by goal and see that three of four are stalled.
They also survive sprints. An epic spans as many rounds as it needs, so the thread of a larger piece of work is not lost every time a sprint closes.
Managing them
The epic manager is where they are created, renamed, given an owner and a target date, and retired when finished.
An epic carries an owner because somebody should be answerable for the whole, not just for the issues inside it. That is usually a different person from whoever is assigned the individual work.
Attaching work
An issue joins an epic from its own form, and can also sit under a parent issue if it is really a piece of something smaller.
Two habits keep this useful:
Attach at creation. An issue that joins an epic three weeks later has already been invisible to anyone tracking that goal.
Keep epics smaller than you want to. An epic holding forty issues tells you nothing, because it is never done and never not-started. If an epic never changes state, it is a project pretending to be a goal.
Seeing progress
Group the board by epic to see the mix, or open the epics tab within sprint management to see which ones the current round is actually advancing.
The uncomfortable version of that view is the useful one: epics with no issues in the sprint are goals nobody is working on this round, whatever the roadmap says.
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