How exactly does Attack work?

[Chrushev]

So is there one stat for Spell/Melee damage? Or do different stats increase different damages? For example as a druid I got Firefist[You must be logged in to view images. Log in or Register.]. Does that increase both my Dmg spell DMG and melee swing DMG? Does it only affect one of them? What about heals? Does it improve my heals?

Thanks ahead of time for explaining this :P