Thus, at creation, you'll be able to choose from three unique classes, a few personalization choices such as hair and gender, and then you're exposed to the game. The meat of the game is handled by your choices within the game itself. As stated previously, the meat of the choices are made within the game itself, and not through creation. It's difficult to answer this question because there are so many components to the system, and they all cross at some point. Let me try.
Character development is stat, skill, level, age, and usage based.
Each time you raise a stat one point, you gain a level. The EXP cost for raising stats increases exponentially. You gain them through a variety of ways. Others you get by becoming a certain age in the game. As you can see, there are many factors involved in how you gain access to Skills and Spells.