Perhaps I'm plain stupid, so please help with this one:
I want to assign custom keys to my F7, F8, F9 and F10 key bars. The game won't let me. I can actually only use the F7 bar. There all of my skills are assigned automatically. It comes that I do have Mana potions assigned to 0 but never any Life potions. I can only use 3 spells on that bar. Using the other ones doesn't work in any way: No spells, no items, no special skills.
Reading the manual I just need to hover the mouse pointer over the regarding magic/ skill and press the corresponding button. Otherwise I could just drag'n'drop that skill/ magic into the bar. The first one doesn't work at all and in the latter case the item or magic is dropped to the ground.
What do I have to do?

Well, works for me like this, you got the fixed bar which is F7, there you will have basic character skills (sneak, traps, weapon skills like enchanted arrows if you use bows, and knockdown if you use meleee, etc, and 3 slots for MAIN spells (which can use buffs) and the last 2 slots are intelligently used for anything that can restore life and mana, the weakest pots go first, like a piece of meat that restores 50 life, then a bigger that restores 250 etc, same for mana potions.
As for F8 till F10, you have to drag and drop your preferred traps and skills DIRECTLY. The only difference with spells, they can only be added to it AFTER you assign them to the 3 slots on your "quickbook", and yes, buffs will not work on them. After you assign the spells on your book, you can take them out and get the ones you use the most back, and they will not disappear from the quickslots.

OMFG ... thanks for the answer ... that's plain rediculous. How am I supposed to be a swift magician if I have to work like this?! :D