I am not administering Jira at my company, but I was involved in the initial setup, so some things here might be somewhat misnamed.
Jira has groups. You can configure who is in each group, what groups are in what groups, etc. You can also integrate it with LDAP (Windows Active Directory).
Jira has roles. Some examples: Administrators, Creators, Developers, Testers, Users. These can be customized. Depending what role a person has, they will be allowed to do different things with the project. For example, if you are a Creator, you can create new issues; if a developer, you can work on issues; a tester can verify issues. For each project, you can pick what users and what groups have the specific role.
So for example, lets say you had the following setup:
Users:
Groups:
- QA Group: Bart, Lisa
- Manager Groups: Homer, Marge
Projects/Roles:
- Intellectual Work
- Administrators: Managers Group
- Developers: Marge, Lisa
- Testers: QA Group
- Users: All Users Group
- Physical Work
- Administrators: Managers Group
- Developers: Homer, Bart
- Testers: QA Group
- Users: All Users Group
- Parenting Work
- Administrators: Homer, Marge
Everything I hope is fairly easy to follow. As a note, neither Lisa or Bart will see the "Parenting Work" Project.