If you are using Jira Software (formerly Jira Agile or GreenHopper), you will see an additional Structure tab in the issue details panel on Scrum and Kanban boards.
The Structure tab displays the standard Structure widget in Pinned Item Mode (highlighting the position of the selected issue and its sub-issues). You can unpin the structure by clicking the Pin button in the toolbar or hitting Ctrl+. (period).
Due to the constrained horizontal space, Structure initially displays only the Key and Summary columns in the Agile tab. You can add more columns by clicking the Add Columns button (the plus sign).
When you click another issue on an Agile board, the Structure widget automatically selects and pins that issue in the current structure. You can switch to a different structure clicking the structure name.
You can edit any field from within Structure widget (just as you can on the Structure Board), provided there's enough space. After you edit an issue, Structure signals Jira to reload the page, and you will see the updated values on the board.