Similar to permission schemes, once you have your security levels in place, you will need to assign users to each of the levels. Users assigned to the security level will have permissions to view issues with the specified security level:

1. Browse to the Edit Issue Security Levels page
2. Click on the Add link for the security level you wish to assign users to
3. Select the option you wish to assign to the security level
4. Click on the Add button to assign users

While it may be tempting to use the Single User option to add individual users, it is a better practice to use other options, such as Project Role and Group, as it is more flexible and doesn't tie the permission to individual users, allowing you to control permission with options such as group association.