Usually, in most light novels, it's only "Just imagine it and pour your mana in, and some nanobot or whatever will make it reality". There are very few that have a clearly defined magic system with defined rules about what is possible and what isn't. Or they have one, but it gets muddied or retconned once the author reaches a point where it gets inconvenient.
I'm reading one good example right now with Zilbagias the Demon Prince. The bloodline magic in this series has a clear ruleset, which is consistent and still in effect 6 volumes in.
