Magic-User. Those who pursue power through the likes of alchemy, mysticism, or witchcraft are magic-users. These men have devoted their lives thus far to the study of magic, so that they may wield miraculous powers through study similar to how clerics do by invoking the gods. While the rewards of powerful spells await them later in their careers, the starting magic-user has but one spell he may cast. He must memorize the spell from his spellbook, and cast the spell that same day or else loose it from his memory. Once a spell is cast, the magical energy actually leaves the caster's body, taking the memory of how to cast the spell with it. There is a chance, however, for magic-users to be able to recall a cast spell – literally holding the magical energy in place with mental prowess. Otherwise, all cast spells must be re-memorized the following night.
A magic-user must have his hands free and be able to speak to cast a spell. Most spells require some kind of material components. Unless specified in the spell description, the components can be presumed to be common items the magic-user can easily find and carry. While the rewards of powerful spells await them later in their careers, the starting magic-user has but one spell he may memorize and hold in his mind ready to cast. He must memorize the spell from his spellbook, and cast the spell that same day or else lose it from his memory. Once a spell is cast, the magical energy actually leaves the caster's body, taking the memory of how to cast the spell with it. Otherwise, magic-users can cast spells while studying them from their spellbooks, but with a casting time considerably longer (15 minutes per spell level).
Intelligence is the prime requisite for magic-users, and they gain benefits for having high Intelligence scores. Humans and demi-humans can all wield magic and progress as magic-users evenly at lower levels. Only at the highest levels do demi-humans slow in their advancement and full-blooded humans begin to outperform them.
All this studying has left the magic-user with little time for martial training. Unless multi-classed, a magic-user does not know how to use any weapons other than clubs, darts, daggers, javelins/spears, maces, sickles, and staves; and is unable to wear any armor heavier than padded armor (and that with a 3 in 6 chance of spell failure) and still cast spells.
At any time, the magic-user may research new spells. The magic-user may research a spell of any spell level that the magic-user is able to cast. Thus, a journeyman could research only 1st level spells, while a medium could research 3rd level spells.
Your DM has guidelines for spell research.
Level Level Title Experience Points Hit Dice Fights As Spells
1 Journeyman 0-1,870 1d4 F1 (1d4) 1 1st level
2 Prestidigitator 1,871-3,750 2d4 F1 (1d4) 2 1st level
3 Medium 3,751-7,500 3d4 F1 (1d4) 2 1st level, 1 2nd level