Also, just to explain how Unknown Armies works a bit as I realise most people won't have played it, it's actually a pretty lightweight system which doesn't bog itself down too heavily when it comes to specific knowledge. At it's core it's a D100 game so you've got a skill level and you're looking to roll a number under than on a D100, taking into account any modifiers the GM might apply.
There are 3 core elements that basically make up your character: -
Meters and skills
... I'll just talk about them quickly here.
Unknown Armies is a social game, and is about cultivating relationships with people. These stats won't come up too much in a one-shot but basically these are people you can rely on, and your dice rolls for success with them become dependant on the quality of your relationship rather than the skill. Even if you're shit at making connections to people, that won't matter with your mentor if you have a strong bond. Each pre-genned character has one Relationship pre-formed, and you'll be able to define two more if you wish.
Meters and Skills
Your core skills and your sanity are balled up into one area in this game and while it's a little weird, it's great. Here's an image in the spoiler of the section on your character sheet, which might help getting your head around it.
Unknown Armies stipulates that there are basically 5 ways that people can be "vulnerable".
Helplessness - A sense of control is crucial for feelings of safety - even if that control is all smoke an mirrors. When you lose the ability to understand how to control a situation around you, the sense of powerlessness can strip away your ability to hold yourself together. Freddy Kruger would attack this first!
Isolation - A subtle danger - isolation corrodes your sanity by denying you input. Without the opinions of others, you can lose the ability to be able to judge yourself.
Self - This is guilt and self loathing. It's conflict between you and what you believe, and this sort of stress damages your ability to believe at all. If you find out in one horrifying moment that your actions mean you're not the person you thought you were, then this can rise very quickly.
Unnatural - You know how you feel when you try to comprehend an infinite thing too long? That's Unnatural. This is the Cthulhu one - where if you're exposed to the universe not working the way you believed, it can start to drive you crazy.
Violence - The game assumes that people have an instinctive revulsion towards violence. It's stressful to hurt others, to see others hurt, or to be hurt.
... All of this pretty much makes perfect sense, right? We want to be safe and stable, we don't want to be exposed to these deeply unpleasant things. You see those Failure boxes? You can only withstand so many mental shocks before you become numb and then insane. Each time you fail one of these checks, you your hollow out a little - and eventually you're gone. It's not pretty, and the roads back are very hard. It also means that you can have a character who is mostly unphased by violence, but starts to go to pieces when they feel like they've got no backup.
But you're not TOTALLY vulnerable to them. Because you know what? You can harden the fuck up, snowflake - facts don't care about your feelings and all that.
You can see that two skills are attached to each meter. and each meter has 9 dots. Lets look at Unnatural specifically.
So you can probably see that by having a score of 60 in Notice, you have a score of 20 in Secrecy, and Vice Versa. In theory, your character untouched will be at the top of the "Notice" side of things. You are curious about the world, you see things. Nothing has hurt you. If some strange thing happens to you and you fail your stress check, instead of ticking off the box, you can choose to Harden Up. Hardening up means you fill in dots equal to the level of the stress (between 1 and 10). So with a completely clean slate, your Notice is 60% and your Secrecy is 20%. Mark off the first box and your Notice is now 55% and the Secrecy is 25%.
Once you mark off that level 1 box, you'll never be phased by Level 1 Unnatural stressors again. You've just accepted it and it can't hurt you any more. Of course, in a longer game, there's only so many psychological calluses that can form before something starts to go wrong with you as a person, but this is a one-shot so there not need to worry about it too much.
I know what you're thinking - "Lying Cat, these skills are incredibly vague, and it's a bit hard for me if I wanted to be an introverted Private Investigator - wouldn't that mean I needed high Notice and high Secrecy? Well, yes. This brings us on to the last section. And probably the most fun.
Your Identity or Identities are who you are. If you were making characters, you would have 120% of points to spend on as many identities as you like, but the more you have the weaker they'll be. These completely override your skills and they can be absolutely anything at all. It's totally freeform, you just need to be able to justify it in conversation.
So you might say "I am a Private Investigator, of course I can Notice Clues at a Crime Scene". And since you probably put 60% into Private Investigator, that means you're not rolling your useless score of 20% on the Meter, you're rolling 60% because that's who you are. Private Investigator is a pretty simple example. One of the pre-genned characters has an identity of "I'm not going to take this shit any more", so you can start to think about what this might substitute for in the world of a shelf stacker. These identities are only vaguely defined in terms of stats, and are about roleplaying. In a longer term game, these Identities improve whenever you fail a roll with them - after all, you get better by picking yourself up and trying again.
So that's the core of it. The strangest part is not being able to define your core skills specifically as they're slightly out of your hands because of your stress levels, but the Identities heap a whole bunch of control and flexibility right back to you, and let you be properly creative with it.