A: The Furthark comes from the Drakes, where the Drakes got it, or get it is a mystery. They are also the only ones who naturally have access to the Futhark, and they grant it to others (Hence how the Aesir and the Jotuns have gained access).
While the Futhark itself is not exhaustible the use of it does make a person tired as if that person just done something phyisically demanding (ex: Lifting heavy equipment). Similar to phyical labor people can train themselves up to more demanding spells, this is a long process and gaining profeciency takes decades (fifty years generally for some of the simpler spells). The Futhark is used by speaking spells or writing certain Runes or combination of Runes.
The Drakes are the sole source of the Futhark and there presence in a dimension is essential to the use of the Futhark, although proximity is not important neither is the number of Drakes (only one is required). The reason for this is one of the mysteries surrounding the futhark.
Also while there is only one Futhark, the Aesir and Jotuns have access to different areas of it. Since the Aesir are "good" they have access to defensive spells and neutral/utility spells. The Jotuns are evil and have access to offensive spells as well as neutral/utility spells.
"Dulce bellum inexpertis."
Official Forum Expert on Norse Mythology
As Odin says in the Hovamal:
"Praise no day 'til evening; no wife 'til on her pyre; no sword 'til tested;
no maid 'til bedded; no ice 'til crossed;
no ale 'til drunk."