I read the descriptions of Staves and Wands in the TWPH but I was left with a big question. From this it looks like you don't actually use charges for these items. They just give you access to spells as if they were known spells even if they are not on your spell list.
How do charges come into play? Do they add a bonus to the spell casting check if expended? I noticed that Mizraith's staff notes how much charges various spells use.