It allows you to create new roles for Dashboard users.
The default role for all new users is User, although the only role you will see is Administrators, only the default user belongs to Administrators.
Only the Administrators role has the necessary privileges to create new roles and users.
The User (default) and Administrators roles are sufficient for most cases and you will not have to create new roles.
From this screen by pressing Edit you can add/remove a user from the Administrators role. Remember that when you create a new Dashboard user this is automatically added to the Users role.