Hi Maxw,
Q:How were they added in Global address book?
A: As mentioned by Gunjan, Party will be created for any customer, vendor, Workers etc. If you delete them party doesn't get deleted unless you set the parameter "Delete parties with no roles".

Q: Is there a way to add someone in Global address book automatically when I create a user in system administration or whatever?
A: No, you have to create a Worker/Employee in HR first and then assign it to User. Of course, you can do customization if you want to.
Q; Also, do you a way to check when was the one added in Global address book and who added the one in Global address book?
A: Name history will give "Modified by" and "Effective date" which is when it was added in the system.
