How does the yellow book affect Dorian Gray?

The book Lord Henry gives Dorian is a kind of symbol of what we would now term the alternative lifestyle upon which Dorian embarks. We are told that

It was a novel without a plot, and with only one character, being, indeed, a psychological study of a certain young Parisian, who spent his life trying to realise in the nineteenth century all the passions and modes of thought that belonged to every century except his own, and to sum up, as it were, in himself the various moods through which the world spirit had ever passed, loving for their mere artificiality those renunciations that men have unwisely called virtue, as well as those natural rebellions that wise men still call sin.

The slim volume appears to be a textbook of "amoral" behavior, particularly involving sexuality, though of course in mainstream Victorian fiction, such as Wilde wrote, this would never be stated openly. From his constant attention to Dorian and his innuendo that invests every sentence, we get the feeling that Lord Henry's purpose has all along been to get Dorian to engage in an alternative lifestyle like that of the young man in the "novel without a plot."
For years, we're told

Dorian Gray could not free himself from the influence of this book.

The book's hero, described as "the wonderful young Parisian" becomes the model for Dorian's own actions and character as he frees himself from the constraints of Victorian society. It would perhaps be wrong, however, to conclude that it is the book alone that leads Dorian on his path. The seeds of change were already within him. This book, just like the fantastic alteration of the portrait, is an influence upon him but also a reflection of what is already happening to him, of the inevitable internal change in character and lifestyle he undergoes.

In chapter 10 of Oscar Wilde's The Picture of Dorian Gray, Dorian lays his eyes on a book that Lord Henry gave him and proceeds to read it. Dorian gets really immersed in the reading, because the "novel without a plot" that it contained revealed things to him that, presumably, lived subconsciously within him.

[...] he became absorbed. It was the strangest book that he had ever read.[...] Things that he had dimly dreamed of were suddenly made real to him. Things of which he had never dreamed were gradually revealed.

When he meets with Lord Henry again, he gives him feedback about the book. The word that he uses to describe his emotion is "fascinated." In fact, he specifically says that there is a difference between "liking" the novel and becoming "fascinated" by it:

I didn't say I liked it, Harry. I said it fascinated me. There is a great difference

We then learn that this fascination lasts, perhaps until the end of Dorian's life. The power of this book lasts for years, and it influences all of Dorian's decisions. It is safe to conclude that the book has, in not so many words, "bewitched" him. Dorian happily allowed that to happen.

For years, Dorian Gray could not free himself from the influence of this book. Or perhaps it would be more accurate to say that he never sought to free himself from it.
https://www.gutenberg.org/files/174/174-h/174-h.htm

The Yellow Book is a major source of the corrupting ideas that will indirectly lead to Dorian Gray's destruction. The book is a kind of aesthete's bible, whose protagonist devotes his whole life to the pursuit of nothing else but the pleasures of the senses. It is an incitement to rampant egoism and selfishness, an open invitation to engage in all manner of sordid activities guaranteed to scandalize bourgeois Victorian society.
Unsurprisingly, it is the louche aristocrat Lord Henry Wotton who gives Dorian a copy of this unabashed celebration of decadence. Yet Henry himself pursues a very different lifestyle than the Yellow Book's protagonist. Dorian, on the other hand, is absolutely transfixed by the utter amorality of the protagonist's approach to life; his utter disdain for the niceties of social convention; and the absolute conviction with which he worships aesthetic sensation as the ultimate god, to which all else must be ruthlessly sacrificed.
Dorian knows that the book is pure poison, yet still finds himself yielding to its seductive, intoxicating immorality. He sees much of himself in the book's protagonist and sets out to emulate his initiation into the cult of beauty, even if it involves the ravaging of his soul by the evil forces his actions unleash. The Yellow Book is dynamite in the wrong hands, so to speak.