A Kindred's Humanity Rating reflects how much of the character's moral nature remains, despite the curse of Caine. It influences how well she may deny her vampiric state as well as how well she can pass for a mortal. Humanity affects things such as how easily it is for the vampire to awaken when danger is present, it affects their virtues (you cannot roll more dice in any virtue than your humanity rating), it affects the length of time the character will spend in torpor and it affects how "human" your character appears.
While Kindred with high humanity ratings are still little more than wolves in sheep's clothing, it is important to know vampires change, as their humanity rating deteriorates... Here is a basic chart, to help:
Humanity 7: Most mortals have Humanity of 7, therefore, vampires with this humanity score are usually able to pass for humans, fairly easily. They also have, like humans, a set idea of what is right and what is wrong... They know not to deliberately kill or hurt someone, they know it is wrong to steal...but they aren't above pushing the speed limit just a tad.
Humanity 6-5: Hey...stuff dies; people break. No... People die; stuff breaks. Oh well. You do what you have to do, right? Vampires of this humanity level won't go out of their way to intentionally damage or injure but, if something goes awry, they aren't overly concerned if they have to do something nasty...that's just what fate has in store for some folks. It is at this stage that the vampire begins to show some sign of the beast; whether it is some animalistic trait or just a faint sense of eeriness that rubs those with higher humanity the wrong way. Either way, their laissez-faire attitudes towards others' rights makes them rather unpleasant to be around.
Humanity 4: Hey man, some people GOTTA die. This vampire is not above killing, so long as the victim is deserving of it (and only the vampire can tell you at what point he thinks others deserving of death...it could just be someone who parts their hair on the right instead of the left). Destruction, theft, injury...no longer are these taboo...now they are tools to get what the vampire wants. Also, while not hideous, in the sense of Gangrel or Nosferatu, vampires at this stage of humanity develop that Bela Lugosi pallid, corpse-like look and most tend to shy away from them.
Humanity 3-2: This Kindred will indulge in whatever twisted pleasures enter his brain. Perversion, callous murder, mutilation and wickedness for the sake of being wicked are the joys of a Kindred with Humanity this low. They delight in the pain of others; the lives and properties of any, save their own, are irrelevant. Few vampires maintain Humanity scores, this low, for long... Damnation is right around the corner and, at this point, it's a welcome thing. Vampires at this stage MAY be physically mistaken for human, but don't count on it.
Humanity 1: Little matters at all to vampires this far gone, even their own desires outside of sustenance and rest. There is nothing a vampire with Humanity, this low, won't do and only a few tattered shreds of ego stand between him and complete devolution. Most who attain this stage find themselves no longer capable of coherent speech and spend their nights gibbering blasphemy among their gore-splattered havens.
Humanity 0: Must sleep. Must feed. Must kill. A character, this low, is completely lost to the beast. Players may NOT play vampires with Humanity of 0.