Helena Petrovna Blavatsky - or HPB as she was known - was a colourful and enigmatic character who she had spent many years travelling and taking a deep interest in esoteric knowledge. She arrived in New York in 1873, where she met Colonel Henry Steel Olcott and they became co-founders of The Theosophical Society, which still exists today.
To find out more about her teachings, you should choose a source which corresponds most with your own beliefs:
If you believe that she had supernatural powers and divine wisdom, visit www.blavatsky.net.
If you believe that she was preposterous pretender and a fraud, read 'Madame Blavatsky's Baboon: A history of the Mystics, Mediums and Misfits who brought Spiritualism to America' by Peter Washington.
Or check out both and make your own mind up.