Managing overall role capabilities can be done by an administrator using Settings > Site administration > Users > Permissions > Define roles. This is the place to add custom roles or modify existing roles. The "Manage roles" tab, allows the system administrator to edit any one of over 350 different capabilities associated with any role. The "Allow role assignments", "Allow role overrides" and "Allow role switches" contain a matrix which give the ability for a specific role to work with other specific roles.
More information on docs.moodle.org
- Moodle Docs Managing Roles - (Version 2.6)