As a member of a project, you can assign an issue to a specific user to prompt any help or feedback by participating in the comments thread of that issue.
To assign an Issue, go to the issue page that you want to assign someone to. In the right-hand column of the page, you will find a section for Assignees. Simply click the + button in that section and type the username.
Learn all about Issues
Discover all you can do with your Issue feature: