Speaking of diatonic scales, what's that? There are two ways to get from a root note up a scale to the same note 1 octave higher. The most common way is the diatonic scale, the familiar do-re-mi-fa-so-la-ti-do (or CDEFGABC). This one consists of what are called steps and half steps. A step is the "distance" between most pairs of notes, say C and D. A half step is the distance between a note and the note's sharp or flat version (C and C#, for instance). The tricky thing about diatonic scales is that most notes are one step apart, but there are two places where the notes are only 1/2 step apart. In major scales, these places are between the 3rd and 4th, and between the 7th and 8th (or octave) notes. In minor scales, the places for half steps are between the 2nd and 3rd notes, and the 5th and 6th notes (I think).

The second way to get from the root to the octave is by going half steps all the way. This is called a chromatic scale, and it has 12 notes, counting the octave: C C# D D# E F G G# A A# B C. That's why the octave is at the twelfth fret of the guitar (or whatever).

Now, I know all this theory, so can't I play worth a tinker's cuss?