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.

Can we conclude that is the dark tower movie just the first book?
no