I read about music theory but I still don't get the use of the CAGED system. I don't see what it has to do with scales etc... If someone could explain it to me in a precise way and not some vague answer, that would be greatly appreciated.

Thanks in advance
I think that by learning the open chords C, A, G, E, and D, you can play any other major triad by moving your hand position up and down the fretboard as a barre chord.
The CAGED system is the 5 positions of the pentatonic scale. If you play each position of the pentatonic scale you will see that they outline the chord shapes C A G E D. That's the way that my guitar teacher taught me, although there may be a different use that I don't know about.
lol wowww

It starts out being the 5 shapes and their arpeggios. From that, you can build the pentatonics, and then the major scales.

If you know enough about theory and you pay attention, you can build the modes from it as well. You can also apply the concept to different types of chords and such, for example diminished chords or whatever. It's a pretty unique way of looking at the guitar, and I personally rather like it.