A musical scale is basically a group of notes with well-defined intervals between them. A musical scale could consist of the notes A, B, C, D, E, F, and G (this is, in fact, a C major scale). Or a musical scale could consist of the notes A, A#, C, C#, D#, E, F#, G. A scale can be any group of notes. However, there are common scales that are used in Western music. These scales are the ones that are familiar to most musicians.
A major scale is defined to have intervals of a whole step,
another whole step, a half step, and then three whole steps followed
by a half step back to the root. Ok, so what does all that mean? A
half step is just a single interval between notes (for example
F to F# is a half step, so is B to C).
A whole step is two
half steps, so it is two intervals between notes (from F to G, or from
B to C#). On the guitar, then, a half step is equivalent to one fret,
and a whole step is equivalent to two frets.
A root of a scale is the note that the scale starts on.
So how is it possible to determine what note a scale starts on?
Let's say there is a scale where the intervals between notes were
defined as whole, whole, half, whole, whole, whole, half (this is
a major scale). Given the notes: A, B, C#, D, E, F#, G
it can be determined that this is a D major scale by looking for
the correct pattern:
There is a lot more that could be said about musical scales.
(musical scales are quite mathematical -- which the reader may or
may not find interesting). At this point in the tutorial, learning
about musical keys and song structure are more important than
in-depth theory on musical scales.