For the best explanation of what all of this Vampire nonsense is about, check out the White Wolf website (which I claim as my internet Bible) - full of everything you want to know about White Wolf, the World of Darkness, Vampires, the Sabbat, the Camarilla, and everything else that this website might be concerned with. But if you can't be bothered with all that, you can read my version here (although I don't pretend that it is anywhere near as good as anything else published officially on the web or on paper).
The World of Darkness is essentially the world we all live in, though it is... darker. Everything that is evil and corrupt is ten times more so, while everything good and virtuous is rare. Think Brooklyn, but the whole world over (apologies to the inhabitants of Brooklyn - in fact, perhaps Lampeter is a more suitable comparison). In the World of Darkness, humans share their existence with others - supernatural beings, from vampires and werewolves to mummies and ghosts. Everything you ever feared but told yourself did not exist, does exist. And they are the least of your worries within the World of Darkness.
Vampires
In the World of Darkness, vampires are real. They are not mere monsters, however, despite the appearances and practices of some. Vampires typically belong to one of the following Clans - groups sharing the same bloodline and general traits. The following is a list of the most common Clans.
Assamite - fearless assassins from the East.
Brujah - thuggish soldiers of the night, once a noble clan of warrior-scholars.
Gangrel - feral vampires with general preference to the wilderness than urban life.
Giovanni - Italian necromancers who deal in organised crime, and the realm of the dead.
Followers of Set - Egyptian vampires who worship their god Set, and seek to corrupt all.
Lasombra - masters of shadow and manipulation, they are the dark aristocracy.
Malkavian - dubbed as merely insane, these madmen have uncanny insight into the world.
Nosferatu - hideous and secretive sewer-rats who harvest information and knowledge.
Ravnos - tricksters and deceivers, claiming their talents from their Gypsy heritage.
Toreador - artisans and socialites, these hedonistic vampires live for pleasure.
Tremere - mystical warlocks that deal in the occult and, more specifically, blood magic.
Tzimisce - Eastern European lords of antiquity that admire etiquette and torment.
Ventrue - subtle manipulators of mortal affairs, they are the epitome of both the Camarilla and the Masquerade.
Caitiff - clanless no-ones, belonging nowhere and scorned for their lack of identity.
The Vampire game that we play is centred around the Sabbat, one of two major sects of vampires. The Camarilla - bitter enemies of the Sabbat - believe that the safest option for unlife is to hide the existence of vampires from mortal eyes, by employing their universal and core tradition of the Masquerade. The Masquerade allows vampires to walk amogst the mortals, interacting (and manipulating) them as though they were humans themselves. The chief reason behind the Masquerade are the torches of the Inquisition - an organisation founded in the Middle Ages, but still going strong in the present day, which is dedicated to hunting down and destroying thr forces of darkness - in this case, vampires.
The Sabbat have no Masquerade, and care not what the mortals see or believe; after all, humans are just "Happy Meals on legs" (to quote a vampire from a different universe). Still, a degree of caution is still employed by the Sabbat, for they too know the power of the Inquisition. But whereas the Camarilla hide their vampiric nature at all costs, the Sabbat revel in theirs.
But the Sabbat have worse fears than the Inquisition. Theirs too is a holy crusade, against their elders. Extremely powerful vampires known as the Antediluvians - vampires that predate the Biblical flood - who, according to the Book of Nod, will one day rise and devour their childer, i.e. vampires worldwide.
Organisation
The Sabbat have a hierarchy or command, which seems a little hypocritical, considering their primary battlecry is freedom from the elders. Still, even chaos needs a degree of order.
The Regent rules over the Sabbat as a whole. In charge of large areas, such as a continent, are the Cardinals. Archbishops and Bishops rule over individual areas or cities, while the Ducti command seperate Packs (small groups of low-level Sabbat). Other ranks within the sect include the Prisci, who serve as advisors and mediators for large areas (and typically rank between a Cardinal and the Archbishops of a given area), Paladins, who serve as bodyguards for Sabbat vampires of power, Priests, who are responsible for the spiritual wellbeing and development of a Pack, and Abbots, whose job it is to guard and protect a Pack's communal haven.
Low-level members of the Sabbat meet regularly, in a designated place known as the Temple, often presided over by the Archbishops, Bishops, or both. In the case of Maiden Newton, Temple meetings are held every Friday night.