In the Dark Tower book series there are 8 books and I was wondering if the movie is covering all of them or if it is only the first one and there will be a movie for every book like in Harry Potter.
No, The Dark Tower film is the first film in a potential series of SEQUEL films and television series continuing on from the end of novels, in which due to the nature of The Dark Tower mythology (that expands into nearly every Stephen King novel), barrows many elements and concepts from the Dark Tower novel series.
The Dark Tower is a 2017 American dark fantasy western film directed and co-written by Nikolaj Arcel. A continuation of Stephen King's novel series of the same name, the film stars Idris Elba as Roland Deschain, a gunslinger on a quest to protect the Dark Tower—a mythical structure which supports all realities—while Matthew McConaughey plays his nemesis, Walter Padick, the Man in Black, and Tom Taylor stars as Jake Chambers, a New York boy who becomes Roland's apprentice.
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.
It's sort of like an adaptation of parts of the first three books (I think). It does leave out a lot, including major characters, and it doesn't have any of the plot points, scenes, or characters from the later books.
It is likely they were planning to make a series of them but are probably not going through with that plan since the first movie was not well received.
It's more like a hot mess with some similar elements to the books.