Issues will appear on the backlog either if you have checked the Backlog box when creating an Issue or if it is a Backlog Issue from Jira. You can drag the Issues here to reorder them.
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You can click on a Backlog Issue to see and edit more details on the right pane.
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The individual Issue details are as follows
Move to the top of the backlog
Move to the bottom of the backlog
Move the Issue to the Kanban Board