Amber is based on a series of books by Roger Zelazny. They're very good. You should read them. But it's not necessary.
Basically, the idea is that there's a "real world," which is Amber. Everything else ... our world, Middle Earth, Narnia, the Star Wars Universe, and any other place your mind can imagine (and more!) exists as imperfect reflections of this world. Not only do the people, scenery and technology level change from shadow to shadow, but so do the physical laws, and those laws which govern magic.
On the other end of reality from Amber, is the Courts of Chaos. The two have a history, of sorts. Originally, all there was was Chaos, then somebody decided to create The Pattern, and in doing so, made Amber. Chaos still exists, and (not surprisingly) the closer to Chaos (and further from Amber) you are, the less ordered things are and the more ... chaotic.
The royal family of Amber can use The Pattern to influence the shadow worlds, and move between them. Basically, the Pattern is theirs, and they can make alterations on how the reflection that they're currently in looks. It's hard to describe everything you can do with the Pattern ... there's a list of "Pattern Powers" in the book, which I don't have handy. If you're thinking of taking it, I'll let you know what they are. If not ... well, then you probably don't know much about the Pattern.
Denizens of the Courts of Chaos have powers for moving through Shadow as well, and (generally speaking) are at odds with their counterparts in Amber. Their power is called the Logrus. Given the ever-changing nature of Chaos and the nearby shadows, Chaosians are Shapeshifters.
Amberites and Chaosians are more real than the people of shadow, who are mere reflections of them. They are like gods to people of shadow ... an average Amberite could go to the Olympic games, and win every event, if they were scheduled so that all could be attended. He or she probably wouldn't even need to rest, as it wouldn't take an undue amount of exertion.
There are also people and creatures in the shadows between, some of whom are quite powerful and may have learned to move between shadows on their own -- often using the Trump power (described below), sorcery, or some kind of magical item.
Amber is point-based. Characters are 100 points ... first comes the attribute auction.
There are four attributes: Psyche, Strength, Endurance and Warfare.
Psyche is a measure of the power of your mind. For the most part, it's what you use when you use powers. The strength of your sorcery, Pattern, Logrus or Trump (and capacity to defend against them) is based on Psyche.
Strength is a measure of brute physical strength, and your ability in unarmed combat.
Endurance is ... well, Endurance. It doesn't just measure your endurance for physical feats, but psychic power-based things, as well.
Warfare is your general armed combat ability. It covers the use of all kinds of weapons, as well as tactics, etc. Swordfights, gunbattles, car chases and chess games all fall under warfare.
There are four basic ranks for each attribute: Human, Chaos, Amber and Ranked.
Human = Average human. What you get from someone with a not-too-horrible diet who watches TV for 4 hours a day.
Chaos = Average Chaosian. About what you'd need to be an Olympic champion.
Amber = Average Amberite. Definitely superior to an Olympic champion -- beyond human potential.
Ranked = Even higher.
Ranked attributes are marked by your score.
You start with an Amber rank in all four categories, though you can sell any of them down to Chaos level (for an extra 10 points) or Human level (for an extra 25 points) should you so wish.
Attributes are decided by auction. You put in your initial bid, and then everyone tries to outbid each other. Remember! You only have a 100 point character. Once you've bid, those points are spent -- you can't sell down afterwards.
After the auction, we move on ...
Pattern Imprint - Basic, 50 Points; Advanced, 75 Points.
The power of Amber, to take this, you must be an Amberite. Allows you to move through Shadow, find whoever or whatever you like, and alter the probabilities of various things happening. The basic form allows you to bend reality into whatever form you like, a la Gumby. The advanced form lets you go further, and even break select rules. You're pretty much all-powerful, if it weren't for all the other all-powerful people running around.
Shapeshifting - Basic, 35 Points, Advanced - 65 Points.
You can change shape. No, this is not some super-fast shapeshifting, it's rather slow and unpleasant to watch. Still, very useful. Basic shapeshifting is just that ... basic shapeshifting. Advanced shapeshifting allows for some neat fucking shit.
Logrus - Basic - 45 Points, Advanced, 70 Points.
Logrus is the power of Chaos, you must be a Lord of Chaos to take the Logrus. Also, you must have Shapeshifting to take Logrus Mastery. Again, it's a bend and break the rules sort of thing. The Logrus is more tangible and a good bit messier than the Pattern. On the other hand, there are also times when it could be considered more useful. Gives most shadow people the heebeegeebees.
Trump Artistry - Basic - 40 Points, Advanced, 60 Points.
Trump Artistry is the power to create pictures (usually in the form of cards) that have a real connection to a person or place. They can be used to contact a person psychically, and/or move from one place to another. Advanced version allows for funky things like Trump Gates and such.
Power Words - 10 Points (for 5 words) + 1 point per additional word.
Little jolts of power at your fingertips! Disrupt spells! Distract your enemies! Give yourself a burst of energy! Impress your friends!
Sorcery - 15 Points
Cast any spell you can imagine (or find in any other game). Spells take a long time to cast, so it's best to prepare them ahead of time, and store them somewhere (an item or the Logrus), because most people don't sit around for two hours so you can throw a fireball at them.
Conjuration - 20 Points.
Make things out of thin air! What could be more fun?
Items and Shadows:
You can also make your own personalized magic items or a place to call your own. These can have any properties you like (and be in any quantity you like). Of course, the more they do, the more expensive they are.
You can also buy things like allies, who can be important people from Amber, Chaos or Shadow. You can pretty much buy anything you want at character creation ... just ask, and we can work it out. Usually.
Have points left over? Take Good Stuff -- it's basically luck (the good kind). Need a few more points for something? Take Bad Stuff! Same thing, the other way.
So, how does this game work? Well, you say what you plan to do, and I tell you it works. Usually.
Basically, it's a roleplaying game, being played across multiple universes in which the characters make gods look like wusses. There's no rolling of dice (which is why it works so well for an e-mail game). Everybody's so competent that it's not necessary. Things don't get left to chance (and when they do -- do you have good stuff, or bad stuff?) One point difference is a serious advantage. If the scores are tied, whoever finished higher in the auction is better.
So, all things being equal, the character with a higher score in the appropriate ability will win in any given encounter. You say what you're doing, explain your tactics, and I'll let you know how it turns out.
That's it. Simple.
You play, you get points. When you think you have enough, you ask for advancement ... either ask for a power, an item, a shadow, or an ability to be raised. Then tack on one of the following:
1. No Bad Stuff.
2. Not willing to go into bad stuff.
3. Will take bad stuff.
If you forget, I'll pick 3.
I figure out how many points you need ... if it's an attribute, it's the number of points you need to catch up to the next player in front of you. As I said, one point makes all the difference in the world, so you're either ahead, behind or tied.
If you have enough points for it, I advance that attribute, and put any extra points into your good stuff. If you don't, then it depends on what you picked:
1. You don't advance, you don't have enough points.
2. I'll take points out of your good stuff to bring you up to the next level, but won't let your Stuff-level drop below 0.
3. You advance, and any points needed come out of your good stuff and/or go into your bad stuff.
Anything bought (powers, items, etc) must be roleplayed ... in other words, you still have to earn the power. You won't know whether or not your advancement was successful until (a) You gain whatever you'd been hoping for, or (b) You picked option 3.
After character creation, you don't get to know your stats. They are a secret.
Any questions? Comments? Things I got wrong? I've got no book on me.
Edited to have the correct point cost for Conjuration: 20 Points, not 25