The first thing you need to do is to set up a new group for your help desk's team members. This will help you distinguish normal Jira users from your help desk staff:

1. Browse to the Group Browser page
2. Name the new group hr-team in the Add Group section
3. Click on the Add group button

You can create more groups for other teams and departments for your scenario here. Since anyone can log a ticket in your project, there is no need to make that distinction.