Not quite a race thing, but an example of how I'd see the magic working.
Conjuring would work vaguely like FMA. You'd take some raw material, rocks, corpses, whatever. Then you'd chant, or draw a circle, or whatever, in order for the raw material to transform into whatever you want.
In reality, highly advanced nanomachines (picomachines? Even smaller?) would be disassembling the matter on a subatomic level and be putting it back together in the form the caster desires. The chant, runes, or whatever the caster uses to make it happen, would actually be instructions in an ancient programming language, the one used to program said nanomachines.
"Leveling up" would be improving your nanomachines or getting new, better ones. As time goes on, you could eventually conjure things out of mid-air, using the air itself as a raw material.