By default, all Stories, Projects, and Epics have unique IDs. These stories and links allow you to link to specific Epics or Stories using URLs.
In addition to URLs, the story dialog also supports linking to individual stories using
This turns into...
You can also send URLs to specific stories by grabbing the permanent link in the upper right-hand corner of the expanded story, or by copying and pasting the URL in the address bar of your browser.