What is the assassin's creed?

At some point in every Assassin's Creed game, the creed itself comes up, but I can never remember what it is. I know it has something to do with "everything is permitted" and there's another part about light and dark. Does anyone remember the full assassin's creed and what it means?

Also I seem to remember Altair losing a finger during a part of his initiation ritual, and some of the assassins in later games have something done to their fingers (removed?) and I seem to remember this having something to do with the hidden blade. What's the story with the fingers?

From The Assassins Creed wiki:

The Assassin's Creed is the code and guiding philosophy of the Assassin Order, upheld from the Third Crusade, until modern days. It restricts unnecessary slaughter of innocents, preserves the reputation of oneself and of the Order, and is meant to create peace, not only within the world, but within the individual.

The three main rules (tenets) of the creed are (also from the wiki):

1. Stay your blade from the flesh of an innocent
2. Hide in plain sight
3. Never compromise the Brotherhood

The Maxim is another part of the creed (wiki as well):

Nothing is true; everything is permitted

"Laa shay'a waqi'un mutlaq bale kouloun mumkin."
("Nothing is true, everything is permitted" in Arabic)
-- The Creed's maxim

The Assassin's Creed is the code and guiding philosophy of the Assassin Order. It restricts unnecessary slaughter of innocents, preserves the reputation of oneself and of the Order, and is meant to create peace, not only within the world, but within the individual.

The Creed mainly emphasizes three simple, moral tenets that focus on ensuring a successful mission, mastery of emotions, and the safety of the Brotherhood.

1. "Stay your blade from the flesh of an innocent."
2. "Hide in plain sight, be one with the crowd."
3. "Never compromise the Brotherhood."

(Source)

Should help you find what it means.

The Blade, is the 'story with the finger'.

The Hidden Spring Blade is 'supposedly' a real weapon actually designed by Leonardo Da Vinci.

The thing is, the design springs the blade up WHERE your ring finger would be in your hand. So to actually USE the blade, your ring finger must be absent. Ie: chopped off.