By pollinating a female plant with a hermaphrodite's pollen. Since the hermie was previously a female, when it's pollen is used on another female plant the seeds are "feminized". Twelve12 is somewhat of a breeding guru, you could go on his breeding program journal and ask him for further information their or send him a PM.
Thanks Stoned4daze61, however I'm not a guru of anything, still a student.
exile19 best way is to get them from sponsor site. Female genetic is actually feminized seeds. So order any strain that has feminized seeds available will do. Regular means the seed can become either male or female. Only get the regular if you're intention is to breed them. Otherwise you'll be wasting resources on growing males. The feminized seeds cost slightly more, it is worth it.
If you're talking about getting feminized seeds from breeding then let me know, I'll point you to the right path. lol