Books
With Experience Comes Wisdom

Books are among the most valuable special items. To spend her hard-earned experience points, Marika will need to find books to read. The EXP cost to read from a book is listed in its page in the inventory screen. Some books have other requirements, such as a minimum intelligence stat or prerequisite skill.
All books are permanent items. Like elixirs and gold, they can only be retrieved from an area once. (On area replays, “dummy books” will be available so that the style points for collecting books can still be earned).
Marika does not have to read a book as soon as she finds one. Unread books can be carried out of the area. This is one reason why you should prioritize clearing an area regardless of score.
Early in the game, Marika should read every book she can find. Eventually, the EXP costs may prohibit her from doing that.
There is no grinding for experience points in Idosra. It is possible to read every book in the game, but probably not without clearing every area with a respectable Rogue Rating rank.
Gaining Wisdom and Intelligence
Wisdom and intelligence are two other common requirements to learn from a book.
The Wisdom (WIS) stat is levelled up via milestones. As Marika learns more about the world, she will gain wisdom.
You can see what objectives Marika currently has by looking in the Status page of the inventory screen. Marika will learn more about the world when she completes objectives. Talking to NPCs is the best way to gain new objectives. If Marika currently has no objectives, then she should find NPCs to converse with!
The Intelligence (INT) stat is increased by spending EXP. She will gain her first additional point in intelligence when she spends 1,000 EXP. Subsequent points in intelligence are gained each time the amount of EXP she has spent doubles.
Tip! Early in the game, Marika will gain intelligence points with every book she reads. This also forces a particular order the first few books must be read in. After the first few areas, she (and you, too!) will have more choices on what order to learn new skills in.