Georgia O'Keeffe knew from a very early age that she wanted to be an artist. When she was just 10 years old, she and her sister started taking art lessons from Sara Mann, a local watercolorist. 
From 1905-1906, she attended the School of the Art Institute of Chicago. Later, in 1907, she attended the Art Students League in New York City. There she studied under well-known American painter William Merritt Chase. In 1908, she was award the William Merrit Chase still-life prize for one of her paintings titled "Dead Rabbit with Copper Pot". The prize itself was a scholarship to attend the Art Students League summer school in Lake George, New York.
Later that same year, she abandoned her dream of being an artist. She felt that she had started mimicking other artists rather than distinguishing herself with her own style. She began a 4-year stint as a commercial artist in Chicago that ended in 1912. 
It was then that she attended a summer school class at the University of Virginia where she was exposed to the forward-thinking ideas of American painter Arthur Wesley Dow. Dow's style of teaching encouraged artists to express themselves through elements of composition such as line, mass and color rather than trying to copy nature. Using the ideas she was taught, O'Keeffe created a series of charcoal drawings where she took natural forms and abstracted them into shapes and lines. She sent some of these drawings to a friend, who showed them to Alfred Stieglitz, a photographer and gallery owner who later wound up marrying Georgia O'Keeffe. 
He exhibited ten of her drawings at his New York gallery in 1916. The following year she had her first solo show at the gallery. Later, in 1918, she moved to New York to devote all of her time to her work.  This was the beginning of a long and varied art career.
The following video is a full biography of her life that is well worth watching if you are interested in learning more about what influenced her work: