SLY

Basically, I wanna know how spellcasting (from mage, sorcerer, druids, etc.) works?
(If you can be thorough on how this works, you don?t have to answer the questions below.)

* Firstly, how can they cast spells w/o mana? Or are they using mana? (I think it should be something like the chakra-thing from Naruto.)
* What exactly do they memorize to be able to cast spells? (I?m sure there?s something more than just chants and hand gestures.)
* I don?t know if this is just gaming rules and not actually applied on the actual world of Forgotten Realms, but why do they have to rememorize the same spell every time before they rest? (I think I can memorize a foreign anthem and be able to recite/sing it for like? hmm? forever? I think if they memorize a certain spell, they don?t have to rememorize the same spell for the next day because the more you do it, the more you get familiar with it.) And is it much better to memorize something ?after? you rest? (not really related, but still.)
* Why do other classes, like fighters and thieves, can?t cast spells or has limited casting abilities? Or do they just simply choose not to be acquainted with magic?
* How does mage casting different from cleric casting and druid casting? (I think cleric get their power from their gods and druids from nature, what about mages?)
* Is a mage?s Finger of Death different from a priest?s Finger of Death spell? If it?s the same, why can?t they do other spells as well, like a non-multiclass druid casting a Spell Trap?
* What difference does their class casting abilities from their innate casting abilities? [Remember the special abilities button (F12) in BG? I believe there are some mage and priest spells there from different kits.]
* What makes a sorcerer a different from your average wizard other than the fact that they don?t learn spells through scrolls? (Is it applicable on their actual world?)

Oh boy, can?t believe how stupid I am. I got a lot more questions and these are just of what I remember at the moment. Hope anyone could me.

Can anyone post a highly detailed info on the BG settings or BG characters (or Forgotten Realms?) for reference purpose of
those who are not very familiar (like me) with it? Or a site where we can find one?