Roles are designed to handle cases where you need to compose, reply to, or forward mail wearing another "hat", for example as a webmaster or a member of a helpdesk team. Using Roles you can specify what will appear in the From: and Reply-To: fields of a message and tailor the signature to the role.
The first time you access this screen it will look like this:-
No roles defined
Selecting Add new role brings up a role entry screen to allow the creation of a new role.
Once you have roles defined these will appear as a list of role names (usually referred to as "aliases") after Existing roles:. Selecting a role name will bring up the roles entry screen to allow alterations to be made to the entry for that role.