each user story can have multiple task (subtask).

[koteswararao]

1. each user story can have multiple task (subtask). Can we have dependencies between these tasks and subtasks so for example if there is bug open for task, someone cannot close the tasks and hence no closure to the user story.

[Joe Pitt]

Yes for sub tasks: See https://confluence.atlassian.com/jirakb/preventing-issues-from-being-closed-while-the-sub-tasks-are-still-open-724928276.html