Question: is the dark tower movie just the first book

Answer: No, Intended to launch a film and television franchise, the first installment combines elements from several novels in the eight-volume series, and takes place in both modern-day New York City and in Mid-World, Roland's Old West-style parallel universe. The film also serves as a canonical sequel to the novel series, which concludes with the revelation that Roland's quest is a cyclical time loop; the presence of the Horn of Eld, which Roland carries in the film, indicates that this is the next cycle.