This feature is available in Catalyst, Enterprise, and Ultimate editions.
For most teams, using the Priority value on issues is sufficient to organize and sort their list. However, some teams might prefer to have specific control over the position of each issue in the list. When in the default display settings, issues are displayed in their rank order. You can change order by dragging and dropping issues up or down the ordered list, or by selecting an issue and clicking Move to Project, which allows you to choose to move the issue to the top/bottom of a page or project.
From the main menu, select Product Planning > Issues.
Select the issue or issues you want to rank from the Issues list, and then click Move to Project.
Select Rank from the drop-down menu, and then choose the appropriate ranking destination for your selected issues (Top of Selected Project, Top of List, Move To Page n, Bottom of List, or Bottom of Selected Project). The system reorders your selected issues accordingly.
See Using Grids for more information about sorting, organizing, and filtering workitems.