The Camarilla is the largest sect of Vampires, a rather loose organisation that tries to enforce the concept of "The Masquerade". Think more or less a Vampire government.
In Vampire: The Masquerade, it is composed of Six (Or seven, if you ignore the End Times books.) Clans. (Brujah, Ventrue, Malkavian, Nosferatu, Toreador, Tremere, and the Gangrel. Their main goal is to make sure the Masquerade is kept in-tact, and there's at least SOME semblance of law and order in Kindred society. Or at least, that's what they claim.
The Camarilla makes an appearance in the lore of Vampire: The Requiem, existing during the time of the Roman Republic and dying out around the time of the fall of the Western Roman Empire. Some of the modern-night Covenants draw inspiration from the factions of the Camarilla or, in the case of the Lancea et Sanctum, claim direct descent from it. It's ancient history unless you're playing Requiem for Rome, which takes place during its heyday.
Overall, the Camarilla basically follow "Traditions". The laws/guidelines that were supposedly handed down from the Big C (Cain) himself. A Brief breakdown of said Traditions is as follows.
1. Masquerade - Keep the existence of Vampires a secret from mortals.
2. Domain - A kindred's hunting ground is his own territory, and he rules it 110% himself.
3. Progeny: Sire only with permission of one's elders. No going around making anyone and everyone you want a Childe.
4. Accounting: Until childer are released, their actions are the responsibility of their sire. Their fuck-ups are your fuck-ups.
5. Hospitality: Honor the domains of others, and present oneself to the ruler of any domain you visit. Don't just waltz in, make yourself known to the Big Cheese first.
6. Destruction: The right to kill Kindred is reserved for the Elder of a community. Only an elder may call a Blood Hunt. I'm sure you can work out what that is.
These traditions more or less form the backbone of Camarilla society, although in Modern Nights the "Elder" is generally interpreted to mean "the local Prince." They care deeply about keeping the whole Masquerade in place, stopping Kindred from going around Embracing every single person they see and making sure that when someone IS Embraced, their sire takes care of 'em. Camarilla aren't interested in deadbeat parents, basically. And finally, keeping vampire society more feudal. The last point is more taken to mean that the older the Kindred, the more respect and authority they should have. This, of course, has pissed off many a young babby Kindred, helping to drive plenty to the Anarch movement instead. Older vampires, of course, support these ideals as it far more benefits them. Especially if they find it harder to interact with the mortal world.
The Camarilla's attitude towards humanity could probably be best described as "pragmatic." More or less dealing with them as sensibly and practically as they physically can. In the Dark Ages, the Inquisition and other mortal forces smoked untold countless numbers of Kindred. Now, humanity's numbers have grown from millions to billions, and they've created weapons that easily overpower vampire powers. If mortals were to find out about the existence of the Kindred, it wouldn't be a difficult task to wipe 'em out. Because of this, the Camarilla has opted for "Let's not let them find out." They also try to make sure humanity isn't harmed by Kindred business (so preferably no mortal casualties when fighting the Sabbat) not because they want to protect the fleshy little mortals, but to keep the Masquerade intact. Kindred are also encouraged to blend in as best they can, to basically hide in plain sight. Not to mention the added bonus of hanging on to their humanity, something the Camarilla, and most Kindred, consider to be important.
The Camarilla was born out of growing threats from the Inquisition and the Anarch Revolt, both of which were causing trouble for Cainite domains in Europe. There had been some attempts at organizing a group of vampires in the past, but not much came of it. The idea of a league of vampires was only taken more seriously in 1394, but a group of elders. However, a bold attack was made by the Anarchs on a castle belonging to Hardestadt of the Ventrue. Fear is a helluva motivator, and as such, the founders-to-be of the Camarilla put together a task-force of their most trusted Childer and servants to get the Anarchs to fuck right off.
The actual formation of the Camarilla was announced in 1435. The name chosen was as it meant it was a group of peers that met in secret, in this case, especially from mortals. The founders began rallying more openly for a coalition to protect fellow Kindred from the dangers of society. Including the Anarchs, mortal lynch mobs, and invading Kindred from the Middle East, known as the Assamite. War continued to rage on in Kindred society for the next couple of decades. The Founders, now called "Justicars," fought hard to keep their new organisation alive. In 1496, the first national conclave was created, during which the Justicars were given authority to punish vampires who violated the Traditions (see above). Also, a new body of agents was also was created to assist the Justicars, giving them more time to better develop the Camarilla. These would later be known as "Archons" and can more or less be thought of as a right-hand man, or even a vice-president.
Finally, in 1493, a peace agreement was made between the still-new Camarilla, the Anarchs, and the Assamites, known as the Convention of Thorns. In this peace agreement, the Traditions were accepted as law by representatives of the clans Brujah, Gangrel, Malkavian, Nosferatu, Toreador, Tremere, and Ventrue. They also joined the Camarilla. However, speakers for the Lasombra and Tzimisce, who were majority Anarchs, were offended by this. They refused to join and rebelled by creating the Sabbat to be a polar opposite to everything the Camarilla represented. In other words, the mother of all Kindred tantrums was thrown.
This event is extremely important because it not only marks the beginning of the Camarilla was we know it tonight, it also was the end of the first Anarch Revolt, and would set the stage for the next five centuries of conflict in kindred society.
A New World
Over the next couple of centuries, many anarchs refused to join the Camarilla, instead opting to join the Sabbat. The group continued to strike out at the Camarilla's power, still upset over the results of the last revolt. However, the larger numbers and proper organisation of the older sect gave the Camarilla a huge advantage over the Sabbat.
In the 17th century, with explorers and the like discovering the 'New World', many younger Sabbat members fled there in large numbers. This left most of Europe to the Camarilla. For a while, there was a bit of debate over if they should chase after them in America. Instead, the idea of taking over new territories was decided as a great idea to start bringing in some new, younger Kindred. For a short time it had seemed that the Sabbat would have/had taken over the entire New World. But they started falling into internal conflicts over dwindling resources. All the while the Camarilla was siding with and gaining power in English, Dutch, and French Colonies. Hurrah for colonialism!
Then came the War of 1812. While human society were fighting said war, the Kindred had their own. The Camarilla began losing more and more of their cities throughout the first chunk of the 19th century. As the war between Camarilla and Sabbat spread to the American frontier, the Camarilla struggled to continue. (Cowboy Vampires?) In fact, they were only able to survive due to civil war within the Sabbat, severely weakening themselves.
The Camarilla began the 20th century greatly weakened by internal disputes, mostly due to Kindred picking different sides during mortal conflicts. Think WW1 and the like. When WW2: This Time It's Personal rocked around, it caused even more troubles. Many elders, particularly among the Toreador, Tremere, and Ventrue, supported the Axis Powers, while the Inner Circle refused to pick a side and many Justicars ended up working against each other. It was a huge clusterfuck, not unlike how WW1 was for mortals. However, when the bombs were dropped on Japan, it became apparent how important preserving the Masquerade really was. And world peace, kind of. If mortals could do that kind of damage to themselves, then they could destroy Kindred just as easily. As such, everyone chilled the fuck out.
Antediluvians and Gehenna
The majority of Kindred in the Camarilla aren't older than a century or two, and as such, weren't alive when the Antediluvian were hanging 'round. Though they could have been educated in the story of Cain and the creation of Vampires, many consider it to be a myth, especially in the modern nights and its advances in science. The leaders of the Camarilla have long made it a strict rule to deny the existence of the Antediluvians, or at least insist that they all died a looooong time ago. Similar to this, any talk of Gehenna (The Apocalypse, more or less) is entirely discouraged and sometimes even punished. They take this shit super seriously. They do this out of the understandable concern such knowledge could result in making a Kindred paranoid, scared, irrational, and maybe even join a Gehenna cult. While barely any Kindred would admit to believing stories about The End Times, many also grow extremely nervous at the signs of its coming. Funny enough, the Camarilla's stance on all this stuff is one of the reasons why the Sabbat hate them. They use it as proof to say the Camarilla are actually run BY the Antediluvians to serve their own interests.
The Camarilla has this little concept they like to call "prestation." Basically, it's a fancy word for meaning 'you scratch my back, I'll scratch yours.' The premise is that if a Kindred receives an important gift or favor, he owes the vampire who gave them said favor/gift. When a fledgling is presented officially before their Prince and recognized as a true member of the domain, they usually engage in their first act of prestation in the process, now owing their Prince.
Some clans, however, such as the Toreador and Ventrue, have Presetation happen even earlier. Favours, boons, and pledges of alliance get around a lot within the Camarilla, to the point where's its just like currency in the mortal world. As there are no real rules or regulations on how they can be traded or used, they're traded around constantly, leading to lines between enemy and friend being blurred. The sanctity of the prestation system is very important to the Camarilla. Especially so to the elders who have spent centuries carefully gaining favors from other kindred and hoarding 'em. If it was suddenly cool for people to just... change their mind, or be able to not return favors, the Elders would be simply fucked. So, of course, the Elders make sure this doesn't happen. If anyone tries to do this, the Elders take it care of it fairly quickly. Instead of killing him, however, they kill his reputation. Using their influence to ruin every single thing he has in his interest. Even if he managed to get through this, pretty much nobody is going to wanna be around him for a long, long while.
As a bonus side effect, Prestation keeps Camarilla society somewhat stable. Very few Kindred want to lose a debt, and thus keep a careful eye on their assets. The outright murder of someone to whom you owe a favor is, simply put, a very fucking stupid idea. Also a super quick and easy way to get a Final Death, so... don't do that. Also fun to note, if an Elder owes a favor to a neonate (no matter how) he is obligated to honor his word. This helps to create the illusion of kindness and readability, and of normal, human-like interaction, that allows the Camarilla to pretend that they aren't damned creatures of the night. Spoiler, they totally are.
The Red List
The Red List contains the Camarilla's Most Wanted, Kindred who are considered a major threat to the body as a whole. They're usually called "Anathema" and their destruction is extremely important if they're seen around. Members of this list are typically powerful, influential, or otherwise extremely skillful. Sometimes, however, it could be a kindred who's just made a gigantic fuck up. Specialized Archons called Alastors hunt the Anathema, and anyone who hangs with 'em. So basically Vampire Vampire Hunters. If they can manage to bag one, they're given a pretty major boon, sometimes called a trophy. Due to the Camarilla looooooving their red tape, there are some requirements and steps for a Kindred to be placed on the Red List.
1. Two Justicars have to agree to prosecute a truly monstrous action
2. Preferably there are witnesses of the deed(s) that have been done.
3. They bring the name of the accused Kindred before the Inner Circle at a meeting.
4. Everyone there has to agree said Kindred is a danger.
5. The Kindred is placed onto the list.
A Conclave is a one of the biggest social events in Camarilla society. It's only allowed to be issued by a Justicar and is usually used as a court for trials, important announcements, etc. Almost like a really important meeting. Because its only used for the most important things, any and all kindred are welcome to attend and share their thoughts and opinions. No matter their age or bloodline (So long as they ain't Sabbat or w/e, of course).
Conclaves have no planned schedule, each Justicar just calls them pretty much whenever he wants. Different codes of conducts are added and removed as they see fit, to better improve the meetings any way they can. Certain arrangements are always made, however, such as seating placement.