It's been brought to my attention that this page has been posted
publically (to the nobilis mailing list). This is fine, but I ought to
point out a few things:
Genre-wise, I'm thinking of a cross between Amber and Neverwhere: the characters are eccentric-but-powerful nobles who divide their time more or less evenly between their own bizarre hobbies, going to dinner parties, scheming with and against each other, and defending reality against unimaginable horrors from Beyond. If you want a feel for the more generic nobilis background (although I'll go over this in the first session or few), you can download two sample chapters from the manual from the publisher's site.
The basic character concept should include a description of your character, both before and after you become a nobilis. Characters are all going to become nobilis in the first session, so you don't have to have a lot of thoughts about what your new life is, but if you want some special physical form (dragon? werewolf? seven feet tall? hair on fire? claws for hands?) that might be a good thing to mention, and some sort of character goals are encouraged also. I should point out that, being as you are a minor deity, "find this guy and take revenge on him" is probably not a sufficiently difficult goal; I'm thinking something more like "create a new continent" or "make human beings aquatic".
Finally, please include the domain you'd like to be in charge of. I haven't played this before and so I have no idea what domains are good, but common sense suggests you want something specific enough to be interesting but general enough to be powerful. If it's something too general, like you want to be the power of Change or Logic or something of that nature, well, be careful of what you ask for, because, trust me, You Will Get It. If you're having trouble thinking of something, here are some suggestions off the top of my head: Locks, Keys, Doors, Ropes, Knots, Faces, Architecture, Stone, Crystals, Fear, Anger, Vision, Heat, Sand, Waves, Cats (or some other animal, or Animals in general*), Cars, Paper, Writing Implements, Confusion, Glass, Blades, Sound, Vacuum, Dust, Smoke, Darkness, Graves, Finance, Hollywood, Computers, Algorithms, Math, Philosophy, Energy, Drugs, Woodworking, Music, Stars, Mythology, Books, Stories, Boxes, Liquids.
*You might ask, why prefer Cats over just Animals, since one is a subset of the other? Well, besides that one might fit the character concept better, the Power of Cats is in fact not a strict subset of the Power of Animals. This is going to be a bit fuzzy and not hard-and-fast, but the more specific powers will have more far-reaching control over their domain. For instance, the Power of Cats might be able to make people move silently, or climb walls, or see in the dark, since those are traditional cat powers. They might be able to control pictures of cats or books about cats or robotic cats. The power of Animals would probably be restricted to controlling just animals, not depictions or variations thereof, and they would have a more limited (but obviously more to choose from) ability to control animal-related powers. Similarly, the power of Emotions could make humans angry. The power of Anger could make buildings angry.
If you're interested in getting a system summary, there are a couple good pages about it on the web. The caveat here is that many of these are for first edition nobilis, which is slightly different in some respects, but they're good to get a general feel for it anyway: