I'm new to the elder scrolls series and im just wondering how staves work? Do you insert a spell in a staff or do they have unique spells already built in?

Magic. :vaultboy:

Already built in in previous games may change in skyrim though, good sir

I think similar to TES4 there will be staffs with spells already, but I hope there will be empty ones too (in Oblivion there was one, but it was quest item)
Even more I hope that without spell, you can use it as actual staff and smack enemies with that (although that seems far fetched)

They're already built in. Just point, shoot, and watch the mudcrabs burn.

anyone know if the Enchanting skill lets you disenchant? If so then that would be really awesome to disenchant a staff and enchant it with your own spells.