As it is in my head (So, quite possibly wrong):
There are 12 notes between any note and its octave (the same note again, but higher)
When comparing 2 notes, you call the distance between them an interval.
Therefore there are twelve intervals between and note and its octave.
They can be laid out like this:
Root | Minor 2nd | Major 2nd | Minor 3rd | Major 3rd | Perfect 4th | Augmented 4th | Perfect 5th | Minor 6th | Major 6th | Minor 7th | Major 7th | Root Octave
From this all scales are made.
For example, the major scale picks out only the major and perfect intervals and groups them together.
ie:
Every note starting with C
Root | Minor 2nd | Major 2nd | Minor 3rd | Major 3rd | Perfect 4th | Augmented 4th | Perfect 5th | Minor 6th | Major 6th | Minor 7th | Major 7th | Root Octave
--C-------C#----------D--------D#--------E--------------F----------F#---------------G-----------G#---------A----------A#--------B-----------C
To form the major scale =
C - D - E - F - G - A - B - C
You could then describe a blues scale as consisting of :
http://www.myguitarworkshop.com/uplo...pentatonic.png
Root | Minor 3rd | Perfect 4th | Perfect 5th | Minor 7th | Octave
Hope that helps, I tried giving as little info as necessary to avoid confusion, but when I figured the above out it demystified scales for me.
If you learn the major scale first, you can then use it as a reference point for every other scale you learn (as in "Ah, it's like the major scale but with a minor 3rd and minor 7th instead of....")
I'd be glad to answer any specific questions you have.