Who is Doctor Howe and what three things does he tell Annie in Act I of "The Miracle Worker"?

Doctor Howe is Samuel Gridley Howe, founder of the Perkins Institute, the first school for the blind and visually impaired in the United States.  Both Annie Sullivan and Helen Keller attended school there.  Doctor Howe is famous for his revolutionary methods for teaching the blind, and reknowned especially for his work with Laura Bridgman, a girl who was both blind and deaf like Helen Keller - he taught her to communicate using sign language and raised print, pioneering the new field of deaf-blind education.

When Annie arrives at the Keller's, she has been studying the works of Dr. Howe.  From his writings she understands that her job - "first, last, and in-between", is to teach Helen language.  In answer to the second half of your question, the play does not mention that Dr. Howe actually told Annie anything directly, although she does remember that he said in his writings, "Language is to the mind more than the light is to the eye".  Also, Annie does say that she has three advantages over Dr. Howe in being chosen to work with Helen - she has "his work behind (her)...hav(ing) read everything he wrote", she is young, and she has been blind herself (Act I).

Who is Dr. Howe in The Miracle Worker?

The Miracle Worker is a play depicting the childhood of Helen Keller, who lost her sight and hearing as a result of becoming ill at 19 months old.

In the context of this story, Dr. Samuel Gridley Howe is a medical professional famous for his work in teaching blind people and for the revolutionary methods that he uses. He is the founder of the Perkins Institute, and is introduced by Annie as someone who “did wonders.” Howe was also the founder of the Massachusetts School for Idiotic and Feeble-Minded Youth.

In the play, we learn that Dr. Howe is extremely knowledgeable in his field. It is partly the fact that 20-year-old Annie has read “every word he wrote” on the topic of teaching blind people that gives her the confidence to think that she can make a difference in Helen’s life.

When Kate asks Annie what she will try to teach Helen first, Annie answers that this will be language. She once again infers her respect for Dr. Howe by repeating something that he had said:

Language is to the mind more than light is to the eye.

Annie notes that Dr. Howe never treated his patients like “ordinary children,” but rather like “eggs everyone was afraid would break.”

Howe was famous for his work with Laura Dewey Bridgman, a blind and deaf child who he had begun working with in 1837. The reason for Annie’s familiarity with Howe’s work is that she too was educated at Perkins Institute, having contracted an eye disease called trachoma at the age of five and being dealt the blow of severe vision loss.

Outside of his involvement with education, Howe was the author of An Historical Sketch of the Greek Revolution, which was informed by his experiences in Greece during the Greek War of Independence.