...yes, a hell of a lot to get your head around really...
...i've learnt through my trade (lithographic), and completely self taught over about 9 years on my own computer, and with software changing all the time, you never stop learning and there is often more than one way to achieve something...
...i've avoided paying anyone to train me, just dived in really and became familiar with the functions as best I could...
...backward engineering other peoples work was something I remember doing quite often at work...
...these days knowing illustrator on its own is rarely enough, with job descriptions requiring knowledge of the entire creative suite, and not just for print graphics but for the web too and maybe even 3D on top of that, with motion graphics too. Some job adverts actually make me laugh sometimes, requesting such as graduated leavers with supposed experience in a commercial environment, minimum 3 years experience. Now apparently graduates don't always go straight into work, simply because they aren't commercially experienced enough, so a bit of a vicious circle for many...
...moving on though...
...linking is essentially where the graphic is seen by illustrator as non-embedded, in that when you open the illustrator file it will need to know where that linked graphic is on your hard disk...
...embedding means the graphic is part of the illustrator file, and hence will make your illustrator file much larger than if it were linked...
...it is generally best to link, although there are occasions when embedding is required, so until you find you have to, just link graphics...
...you can re-link an embedded graphic using the links palette, flyout menu, if need be...
...a good place to explore is the Adobe Video Workshop here:
Andrew