For Yellowfin to provision users automatically it has to assign a role for them. This role is defined as a Yellowfin Default role. This means ALL new YF users are given this user role that is set as default.
In order to select a role as the default, open the Administration panel and expand the Roles option. Select the role you wish to make the default role by clicking on the hyper linked name. This will open the role for edit purposes. Then tick the Default Role check box. (see example below)