DM:
Learning Spells
Magic-Users start the game with a spellbook containing two 1st level spells and one 2nd level spell, and do not automatically acquire new spells as they advance in levels. New spells are learnt as listed under 'Creating New Spells', even if picked from the standard list of spells. The primary benefit of researching a spell as published in the standard list of spells is that the 15% chance of failure from researching a new spell doesn't apply.
Characters who have access to materials such as deciphered spellbooks or scrolls may copy those spells to their spellbooks as if recreating lost but well-understood spells - the primary benefit of this is reduced time.
The rules:
Creating New Spells
The player should describe in detail the spell they wish to create and the effects it has. The referee will then decide if the spell can be created and, if so, what the spell level will be.
Restrictions
The character must be capable of casting spells of the level the new spell will be.
Cost and Time
Researching a new spell takes two weeks per spell level and 1,000gp per spell level.
The rules:
Lost Spell Books
A magic-user can rewrite the spells in a lost or destroyed spell book:
Cost: The cost per spell to be recovered is 1 week of game time and 1,000gp per level of the spell. For instance, rewriting two first level spells and one 2nd level spell will take 4 weeks and 4,000gp.
Sole activity: This activity requires complete concentration. The character may not engage in any other activity for the required period.