if its a spell you already have, say -fire dart-, it wont level up per-say, but after hero level ups you get a few points each time into your spell mastery i believe.  early on it wont be a huge change, but later on that same spell will do quite a bit more damage and it will be less likely that the other guy can resist the spell.

on the second, thats kinda something youll have to figure out on your own. There are so many ways to get stats from so many different things Id be here all day.

Its a great game once you get the hang of it.  Good luck.