tarot heart
If you want to understand the GT, Iris Treppner's course is excellent. Absolutely excellent. You can find it here. This site is in German but her course is available in English and German. You can also find a wealth of information (in English) about the GT, other spreads, meanings and a lot more here.
Both of these sites offer the very best information on the Lenormand currently available in English.
Yes, Tag is correct once again. The Treppener course is excellent and what I used to learn. Highly recommended! Also, Andy's website is an excellent resource. I also like Malkiel Dietrich who you can find on youtube. I really like that he is all Lenormand and playing cards. He doesn't do tarot at all. I really like him for that. Tarot people find it too difficult to not mix the two systems.
Stay away from tarot people who are hopping on the Lenormand bandwagon with little experience. I have been reading Lenormand for over 4 years and I would not dare to call myself an expert or put out a book. It takes time and practice to achieve a level of expertise before you can teach the stuff. Just my two cents.