Hi Camilla, welcome to the site! I've actually been a Full Access member for a number of months, (I'm switching from Paypal to my credit card, so right now my membership is just registered user) and I second Carmine's advice, so you can stop reading now, or continue as I give a super-long winded explanation that hopefully will set you on the right track...
First off, its great that you have such a clear goal. The artists you listed are very good at guitar, and are playing at a very advanced level... but just like you they started off not knowing a thing about guitar, and got to where they are today with some talent but really just a lot of hard work. If you have an XBox, you can go ahead and Craigslist it right now... :) Really though, you're aiming high, which is great, but to get there you're going have to really dedicate yourself and be prepared for a long haul. The good news is you'll have a ton of fun getting there, and you're really at the perfect age to do this.
Normally you'll get advice like "learn chords" or "get to know the fretboard" which is all true, but lets get you zeroed in on the path to playing like those guys, ok?
1) You need to know how to practice. Watch videos of those guys playing. It looks easy for them doesn't it? Well, it is. How can that be though when what they are playing sounds so complicated? Its because they started with really basic fundamentals, and built their skills up slowly over time. Anything you learn you'll need to play it slowly enough so that you play it perfect or near perfect pretty much all the time. Don't practice sloppy. Take new chords, make them simpler if you have to, and practice them very slowly so you never make a mistake. Chris has a video on this site that explains this principal really well. As you get better with the chord, you can start playing in time (with a metronome) and add any fingers you may have left out to make it easier on yourself, until you get to where you know the chord really well.
2) The artists you mentioned are playing fingerpicking style. Antoine is using finger-picks, which are picks for each finger, but both guys are fingerpicking, rather than strumming (though they add in strumming from time to time). So, you'll need to know some basic chords and how to play them perfectly, and some finger-picking patterns. Notice I'm not talking about playing fast, just playing perfectly. Speed will come with time.
Lisa McCormick's "Fingerpicking for Beginners" is an awesome course on this site, and it will get you going in the right direction.
3) Adding complexity: there is a very specific technique that these guys are using that really gives them that "OMG how are they doing that on one guitar??" sound. I'm no expert, but I believe the technique probably developed with the "Chapman Stick". Essentially, they are using their left hand, the hand they fret notes and chords with, to sound notes in addition to fingerpicking with their right hand. Take a look at this video where Andy starts of not even using his right hand at all, he's only using his fretting hand:
http://www.youtube.com/watch?v=3grSSc4OrGc&feature=grec_indexSee how he is pulling off on the strings, and then fretting them to make the notes sound? This technique is at the heart of their style & sound. The other thing they are doing is sort of slapping notes with their right hand to give it a more percussive sound. Check out this video of Chapman Stick to get an idea of what this technique is all about:
http://www.youtube.com/watch?v=PvuiAobq2_YNow go watch this one:
http://www.youtube.com/watch?v=uNw9YaXemlMYou can see that even though the instrument is guitar, its virtually the same technique.
"Hammer-Ons" and "Pull-offs" are two techniques you'll hear about a lot in guitar playing, its just these guys have taken it to a very advanced level to create a unique sound.
Ok, if you want a very simple taste, try this... first, make sure you know the open chords A minor and C major. Make sure you can play them flawlessly, no buzzing strings or muted notes, and that you can switch back and forth between them while staying on the beat. You don't have to play fast. Now, look at the A minor chord: your second finger is on the second fret of the 4th string. The note it is fretting is E. Switch to C major. Your second finger stays in the same spot, fretting the E string.
Strum the A minor chord slowly, and then with your second finger, pull-off of the string, and then fret back down on it again. Make sure that your other fingers fretting notes don't move or mute strings. Go as slow as you need to to make it work. So what you are doing is strumming the A minor, which includes the E note on the fourth string 2nd fret, then you are pulling off with your second finger to sound the open string, D, then "hammering-on" to sound the E note again. Its really important that after the strum, the D note and the E note stand out as individual notes. Remember that the act of pulling off of the string and then fretting down hard again is what is making the note sound. Once you can do this, try switching to the C major chord and doing the same thing. Play the A minor, then the C major continuing to hammer-on and pull-off on the D string. Notice how you can make the hammer/pull-off sound "separate" from the strum. This is just a tinsy winsy tiny glimmer of the beginning of what those guys are doing. Once you learn some fingerpicking patterns, you'll be able to use this technique to add complexity to your sound. The real art form is in discovering which picking pattern to use, and how to combine it with hammer-ons and pull-offs. Then there's the whole slapping with the right-hand which I would worry about later.
One thing to note... you can start learning this style right away. But make sure you play in-time with a metronome! I met a guy who played this style, and he was super super sloppy, could not play in time at all. He said that he'd never found a guitarist that was "good enough to play with him" but the reality was that he couldn't hold any kind of tempo at all, and honestly, all his slaps and pops just sounding annoying. Its way better to be able to play something simple, and slowly, than to try and be too complex too fast too soon and just be muffing it up all the time. Join up, go through Lisa's course, and see how you feel after that.
Good luck and let us know how you make out!
Cal
cm