The Agile Board Inserter allows you to add issues (epics or all other issue types) from an agile board.
You can select from any Agile Boards that you have access to. Once you've chosen the Agile Board, select whether you want to insert epics or all other issues (stories, bugs, tasks, etc).
Once you've made your selection, click Apply. The inserter should now appear as a new row in your structure, with the added epics or issues placed below it.