Originally Posted by: metal.totoand another question, do i have to memorize every scale of the notes or i just have to understand how they are made and remember their formulas? :D

you dont need to learn every single scale there is. that would take years and would be very dull and if you ever actually finsihed you might not even be able to play the guitar afterwards. do you think even the best players here memorized everything? that why we learn theory, so we dont need to learn every thing.

the circle of fifths is one tool you do need to learn. but ill help you with a little major scale trick i know.

in the key of C a I IV V progression is C F G (they are actually 7th chords but its ok for now)

that gives us the scale notes of C F G ,easy.

the notes of a C major Triad (a 3 note chord the basis for most c major chords) are C E G or 1 3 5. the 1st note the third and the fifth.

that gives use the scale notes of C E F G.

for the 7th note things get complex. the 7th note of a major scale is always a half step below the 8 th note (the root note same and the first note) so that makes it a B

so now we have the scale notes of C E F G B
follow me so far?
the 6th mode of every key is the aoleian also know as the minor scale. in the case of C which note is the relative minor? if B is the 7th what could it be? well now we apply a new 'formula to our scale. W means whole step and H means half step. so here we go:

WWHWWWH


following that formula we know that A is the 6th note and if we use it to figure out the second note we find D as the second note. so now we have C major

C D E F G A B.

it goes alot faster in my head, this way might not work for you but im sure you can find your own way.