interface trouble - how do i fill my skill bar?

ok so youve bought the ability then all you do is left click on the ability in the bar then left click the target if the target is in range and thats all you have to do

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.

OK, you purchase a skill.

Certain skills are passive, meaning you cannot activate them. Sedna's healing wind for example automatically grants health per second to every allied unit in range. Regulus' sniper scope ability increases his range, and there is nothing you need to do.

There are 8 "normal" demigods who have 4 activateable abilities. Using these abilities is relatively easy. Most require you to choose a target after clickng them (fireball, penitence, pounce) but some just go off like surge of faith or circle of flames or fire nova etc.

The other 2 have form switching, 3 abilities in mode 1, 3 more in mode 2 

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

demon assasin has only one form he only has 4 active abilitys the rest are passive

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 ^^;

Don't feel bad man. I felt sort of the same way when I first got the game. I was pretty puzzled that I only had 4 abilities...

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.

No, it wasn't about the consumables, but about the ability tree.