[mrpaint]

As you requested here, I assume you were asking about YAFB so all the answers are for YAFB only.

1. A user account is created if you enable the Register On-the-fly feature. Otherwise, that user must go through a simplified registration process
2. If you use the Register On-the-fly feature, usernames will be generated from predefined patterns (set via AdminCP settings page). If user goes through simplified registration process, they can choose their own username
3. They can change password and use the standard vBulletin login method afterward.

Please note that, all the answers are for YAFB. I have no idea why shaun2222 didn't post these questions in the thread but I hope it's appropriate for me to answer here. Thank you for reading.