What am I missing? I've read through the manual and done several searches here, but I must be the dumbest person in the world because I can't figure out how to throw bombs or powders during combat. I've tried equipping them to a free hand...no good. I've tried using them during combat, but I can't select and enemy group and they just end up being cast on my party...no good.

Any guidance is greatly appreciated! Thanks!

It's a lot like casting spells in combat:
Select the little box next to your character's portrait, which pops out into a menu with weapon, shield, spellbook, etc in it. Select the hand. You'll get a menu of all the items in that character's personal inventory that can be used now. Select the bomb/powder you want to throw.

Thanks Scatter! I'll give it a shot.