I strognly agree with the book recommendations pagan and Isisa brought you, I have read both these book and they're wonderful and informative for beginners of herbalism and also for other experience levels... And as said, searching in Google or other search engine lessons about herbalism is very recommended.
But, I would like to add here something.
Othala , a friend and a member of this site has an amazing website about herbalism, it is called herbal wisdom. Here's a direct link to the site:
Note that the site is still being developed, but i can assure you that Othala will make it great and amazing as always ! It's just a brand new site and is all about herbalism :)
Feel free to join it, read the information given by othala, participate in the forums and ask questions whenever you wish. You won't be sorry.
Note: this hasn't been posted for advertisement and site development purposes, this is only a recommendation in answer of the question for the person who opened a thread