Little was known about the Wicked Witch of the East. In the books, it is unknown if she is related to the Wicked Witch of the West, but in the movie they are sisters. We do know that she was an enemy to the the Good Witch of the North and Glinda the Good Witch of the South. She was a wicked leader to the Munchkins in east parts of Oz. She was also the reason the Tin Woodman was cursed, chopping off his body and becoming a cyborg creature.
When a twister came to Kansas and swept the Gale's home to Oz, it landed on the Wicked Witch of the East killing her. Dorothy Gale was reward by the Good Witch of the North the evil witch's silver slippers. Thus, Dorothy began her adventures in Oz.