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). Don't worry if you want to include both – select one for now, and you can add the other using Extend or Group generators later.
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.
The Agile Board Inserter is a particularly useful way to start a more complex structure.
Here's a quick example of what that might look like: