#1
What are they? and whats the difference between 500k and 250k? I might be an idiot for asking but I want to know.
#2
It controls how loud your guitar is, duh.

A 500K pot will be brighter than a 250K pot because it will bleed less high frequencies to ground. 500K pots are most common on guitars with humbuckers because they usually need some help in the brightness department.
In the Oven:

18 Watt!