Manuals of [Skill] are rare books which greatly speed the rate at which you train the skills they pertain to by applying a +4 bonus to your skill aptitude. Manuals are activated by reading them, and deactivated by reading them again or dropping them. Each manual has a limited amount of extra XP they can provide: once that amount is reached, the manual is destroyed.
You can only study a manual if you have access to the skill it teaches. Weapon skills require an appropriate weapon in your inventory, the Armour skill requires you wear some form of restrictive body armour, and magic skills require you know spells in the appropriate school.
This is a manual of [Skill]. Do you want to study it?
You start studying [Skill].You have finished your manual of [Skill] and toss it away.
You stop studying [Skill].
Tips and Tricks
While manuals do essentially generate free XP, they only do so as you train the skill. If this means ignoring a skill that's useful to your character in order to train something you don't really need, it may actually be harmful to use. Furthermore, because of the antitraining penalty of some magic schools (Fire/Ice and Earth/Air), it could become impractical to train a skill which opposes one which you exploited a manual in earlier.
Users of manuals may want to add this to their Options file Init.txt (see Options_guide.txt):
force_more_message = finished your manual
This will alert you when your manual's skill aptitude bonus has run out and allow you to readjust your training priorities should you desire.
Prior to 0.9, manuals functioned very differently because the skill system was very different. They would allow you to assign stored up experience from your experience pool to a specific skill without actually using that skill, and would crumble to dust after sufficient uses.