So, the thing is this:
I am currently the GM of four unfortunate souls:) I am pretty new to shadowrun, and no one but me has even heard of the game (i'm sort of a missionary in this context). I got the bacics down, but i get confused when things get complicated. Awakened world is halfway done and the matrix section... if any one of my players decide to hack into somewhere i'll spontaneously combust
I know that given enough time and practice anything is possible, but sometimes i feel like i'm preparing for the finals rather than reading a rulebook. As you can guess, that defeats the whole "having fun" concept.
Even worse, my players knows squat, which means i have to teach something that i have learned just now. They all have sr4a pdf (some have all the books), but are reluctant to read through the whole book. The good thing is all of them are veteran players and don't have munchkin urges (usually). I limited them to the main rulebook.
An example: It took us about 6 hours the create 3 characters (fourth one was sick). And they still have some finishing touches to take care of. And one them is thinking about recreating the character. And they already had the general idea (street samurai, dwarf with shotgun, hacker, gun adept). The game hasn't started yet = they know nothing about rules.
Any help is appreciated.

p.s : if any designer is reading this, please don't get the wrong idea.

Hacking typically requires all sorts of agreements and rulings. I'd fake it with an NPC until the rest of the game is working and everyone understands combat and magic. Fake it with drones, don't go deep into the rigging mechanics. Just keep the drones under control, they can dominate a game if the GM lets them.

Magic: If you don't have any mages don't include a mage or an awakened critter in the opposition for the first few runs, then you don't have to worry about sorcery or summoning rules, astral stuff, wards etc. The adept part of magic is pretty straight forward.

Have people write down (and you should have too) their weapons, appropriate skill and mods for them. I've seen people spend minutes trying to figure this out in a combat (paging though the books etc) if it isn't done up-front.

Aaron has a couple of cheat sheets that people have said nice things about.

Many years ago I was in the same situation when Shadowrun was first released, and only one of my players had any role-playing experience and I had the only rule book just to make things even more difficult (no pdfs then, hell none of us even had a pc then).

So the first thing I did was get them to pick an archetype each, write out the stats and then I got them roll initiative and shoot each other. I had them do this several times each time swapping archetypes, each time introducing stuff like different armour, burst fire, different types of gun, ammo etc. Then I did the same using spell magic. They spent hours trying to kill each other and really enjoyed it. Then I got them to make their own characters and I ran the First Run Food Fight scenario at the back of the book, by that stage they had the basics down.

We never really used the matrix rules, I just fluffed them as I went, but i imagine you could apply the same kind of idea to them.

I think that, as a GM. you don't need to know everything, but at least have a pretty good idea. For educating myself on 4th edition, I created 2 characters by myself (a weapons specialist/adept and a hacker) and played what I call "Shadowrun Solitaire"... setting up small combat scenarios and letting my new characters duke it out with a few NPCs pulled from the contacts/adventures book. This helped me learn how the rolls worked.. and what modifiers I was always forgetting. Once I understood what was going on, then I used "cheat sheets", like this awesome mod calculator... http://www.supernerd.com.au/~edenhome/sr4_modifiers.html . But, again, I thought it was vitally important that I had a working knowledge of the rules BEFORE I relied on these tools. Teaching the game to others is tough, but I think the best thing is to jump in the pool and play. Honestly, I think the only required info for a newbie player to read is the Welcome to the Shadows, History..., and the Game Concepts chapter., and that all could be read in an evening or two. Encourage players to get the physical SR4a book, if, like me, they get fatigued fast by reading a PDF file on a computer screen (Plus, the SR4A book is beautiful, anyway. everyone wants it in their bookshelf.) If players need help creating characters, I would meet 1:1 with them and get them going. Using Daegann's SR4 character generator tool cuts down some significant creation time, but you still need to allow an hour or so to transfer all that stuff to a properly organized character sheet. However, it is time well-spent, as the player and GM get to review all the work they did on building the character, and double-check all those bonuses. When everyone is ready to play, verbally review the high-level info from the game concepts chapter (types of tests, etc.), maybe make a few demonstration rolls, and dive into the story. They will get the hang of it after a few sessions. When playing, let them have fun: don't say no, or that they cannot do something, let them roll for it and sweat your high thresholds. If you screw up (and we GMs always do; don't tell anyone), have a good laugh and move on.

I'm not sure who came up with these and I want to give credit where credit is due, but: http://pavao.org/shadowrun/cheatsheets/SR4CheatSheets4up.pdf
That is a stack of step-by-step instructions for most common tasks.

My advice is to make sure you keep it simple. I tried to drop my players into an open-ended investigation mission with multiple ways to get the goal and it went south in a hurry. If you're not going to use one of the pre-written scenarios (Food Fight?) then I suggest you make sure to run them with an NPC who can steer them in the right direction, and keep the first mission really simple. Somebody hiring the heroes to take out a rampaging street gang, for instance - a few minutes of roleplaying, set up an ambush, and then a brawl.

Cheat sheets are good idea. And errata, if You have not an Anniversary Rulebook.
I recommend (as always) to grab Unwired and read "Matrix Topology" section - just about 10 pages, but it helps.
It's a good idea to do some digging at Dumpshock Forums after a few game sessions - there are some controversial issues alredy discussed here.

My first SR4 session was long and slow... I was in pretty much the same boat as you were. I had read the book a time or two and had some players create characters, which was only two player in the first session (and it took 2-4 hours to get each of them done from scratch).

For a first session (or two), I'd go really simple. Focus on a couple combats. Get everyone used to rolling dice to shoot people and get shot at and if you are feeling really good, try throwing in some melee (with or without weapons). Just get everyone used to what dice pools they will be looking at rolling and you get used to what sort of modifiers you'll need to be aware of (even after 2 years of SR4, I still have to run down the list of modifiers each combat).

I would stay away from magic and the matrix the first few games and then slowly bring them in based on your players' interests. I am in my second campaign with my group, and both had hackers. We are just now finally deciding to scrap the hacker and just rely on me NPCing the matrix as needed, as it is easy to bog the game down if everyone is not interested in the matrix side of things.

And remember, the general rule is everything is a skill + attribute roll. As the GM, you assign the threshold to accomplish the task (1 is easy, 2 is average, 3 is hard, 6+ is extreme) and anything the beat by 4 or more is a critical success. So, when you get bogged down with the rules and are not 100% sure what to use, just make it up using that general rule (and maybe ask a player to look it up, so when it comes up again, you'll have the right rule). The game will be a lot more fun if you just keep it moving, rather than get bogged down in all the specific rules. Over time, you'll pick up the right ones...

thanks for all the help
i have sr4a (god it's beautiful), but it costs 70 us dollars and takes about 3 weeks to get it here. i was planning to print out relevant areas though.
is the mod calculator up to date? there were a ton of erratas since 2005, so i'm a bit paranoid on the whole issue:)
the hacker is a redneck and the dwarf owns his own roadhouse, so i don't think violance will be hard to come by.