[chrzone]

There are a number of automatic bars the game gives you
that maps to the keys 1-9 and 0

However, you can reassign them

I use the one i get to by F8 key

Then open inventory 'i' key (or spells etc)

Then if something is already assigned to say key '1'
then RMB (right mouse button in the tool bar) and it is emptied

Then simply drag the weapon, potion or whatever EXACTLY
on the middle of the box corresponding to key 1. On highres screens
it can be hard to get it exactly right since the item is usually larger
than the box

Then release LMB once over the empty slot

and now that key selects/equips whatever you dragged there