Huh. I'm at work right now so i can't test it, but i'm a bit confused now. The skill bar, iirc. has 4 slots. Indeed some of the buyable skills are preassigned to those slots, so if i buy those, i can use them. But every DG has 10 or so skills. Some are not on the slots. I DID notice that some of them are passive, but are there only 4 active skills per DG? For example, when i was playing demon assassin, i bought some sort of healing skill (lower part  of the page) and i don't think it was a passive skill, but it wasn't on the 4 slots either. But there's a possibility that i misread it.

I see. So there is no need to define the skill bar. And the demon hunter is probably one of the form switchers, since he's not in the manual and was, i believe, added after i updated the game. Which could explain why i couldn't access that skill because maybe it was the wrong form (or maybe it WAS passive).

ty both

Yes, i found out. I'm home now and i do feel rather stupid. The "heal" was in fact the increase in health, the one that apparently every demigod has ^^;

are you talking about the consumable slots? you can buy various things from the shop like potions and teleport scrolls and they will show up in the UI than you just click the slot to use it.