They don't work!! there is no scientifical proof that herbs can make you cock grow. SOme of those herbs will promote a better blood circulation to your penis and will make it look "bigger" while flaccid but not because the actual tissue grew, but because there is more temporary blood down there. Those herbs will also make you hornier so you'll be most of the day with a little hard on and that will give you the impression of a bigger cock too.
The only proven thing is excercise; takes years, but it works.