Discussion of the Necropolis faction.

I have a question: when a hero levels up, they receive points to spend on combat skills, magic, or personal hero skills. Could you explain how personal hero skills are leveled up? I've leveled up to level 10 and can't seem to increase the Necromancy skill. Also, in battle, a hero playing as a Necromancer can resurrect units using the Necromancy skill bar, not magic. But what's the difference if I use only a quarter of the bar or the entire bar? I've tried both ways, and the result is the same...