"Roles" are different sets of responsibilities your users can have concerning the resolution of issues. Creating different roles allows you to segregate the responsibilities and permissions each user can have.
You can create up to five different roles for managing various aspects of active cases. Note that you can allow the same roles to have different permissions and groups by using multiple workflows.
Note that the same role may need different permissions - what the role is allowed to do - for different workflows. Permissions for the role are therefore set for each individual workflow when the workflow is created. See Workflows
Roles List
Your project comes with two default roles:
Case Manager - typically used for the user who will be expected to "manage" cases, review and resolve.
Watcher - typically reserved for users who should stay informed of the progress or status of a case.