The role portlet is dedicated to create and edit roles. A role will be used to grant different permission level to different portlets. A user can have several roles (for example he can be an administrator of a category of forum but only a reader on another category)
To create a new role, you just need to define a short name that will be used for reference, and a display name for displaying to the user, for example admin would be a good name for the display name Administrators, changing the display name will not affect the security rules
While editing a role, you just need to pick an exising role then change the display name.