What is some important information in the book The Alchemist?
This question is quite broad, so I'm going to stay broad as well. I'll try to highlight some important plot movement and basic literary techniques used in the novel.
One important detail to notice is that the book is written from the third person omniscient point of view. This means that the narrator is an all-knowing outside observer. He/she knows all of the characters thoughts and motivations. This point of view allows the reader to be a bit more detached from the characters as well.
The story is also told in the past tense, which helps it feel and read like ancient myth or fairytale.
The setting of any story is always an important detail. The Alchemist does not ever give a specific date, but the reader can assume the story takes place before any "modern" time. There aren't any cars and things like that. As for place, the book moves from southern Europe (Spain) to Africa and the Sahara Desert.
The protagonist is Santiago and the antagonist isn't really a specific person. The main conflict is between Santiago, his journey, and himself. There are several times that Santiago could stop his search for the treasure and be happy, but he wills himself to complete his quest.
Another important piece of information in the story is Santiago's obsession with and envy for the wind. Why is that important? Because it foreshadows his future ability to transform himself into the wind.