I quickly googled the title and surely Wikipedia has a write up about it. It goes on to say Green started work as a postal carrier in Harlem, New York. In the 1930s, he began to collect information on stores in the New York area that accepted black travelers, and published his first guide in 1936. It was so popular that he immediately began to expand its coverage the next year to other US destinations. After retiring from the Postal Service, Green continued to work on updating issues of The Green Book, and building up the related travel business he had established in 1947.
He created a publishing office in Harlem. In 1947 he established a Vacation Reservation Service to book reservations at black owned establishments. By 1949 the guide included destinations in Bermuda, Mexico and Canada and listed food, lodging, and gas stations. In 1952 Green changed the name to The Negro Travelers' Green Book. His travel bureau operated at offices at 200. W. 135th Street in Harlem, New York.