Issue structure is displayed by the structure widget, which is located in several places in JIRA - on a dedicated Structure Board, on the issue page, on the project, component and version pages. The widget displays a scrollable grid with the hierarchical list of issues and lets you work with the structure as well as with every issue.

Most functionality of the structure widget is the same on every page, however there are few specific things that the structure does on an issue page and on project/component/version pages. You can work with the structure on the page that's most convenient for you:

See also: Working with the Structure Widget