Read the Intro to Sharps for a more basic concept.
The musical notes have the letters, ABCDEFG. These are not all the notes we may hear in music. To name the sounds between the letters, we must add sharps or flats.
We may play a song in different Keys. The Key tells us which notes to sharp or flat. The Key's name is based on the first note of a song's Major Scale, or its Root. If a song is based around the 'A' note, then 'A' is our Root. (We're using Major Keys.)
The above scale is the A Major scale.
"...the Root note is the name of the Key, and the Order of Sharps or Flats are tools to find the number of sharps or flats, for that Key."
These notes are in a song written in the Key of 'A'. There are 3 sharps, F# C# G#. The note, 'A' is our Root, or 1st note.
Since the A Major scale has 3 sharps only, then these 3 sharp notes must make the correct sound for a major scale. How can we find the correct number of sharps for any major scale, starting from any root?
We must order the sharps to any scale with the following pattern:
With this Order, we can find the Key for any major scale.
This is done with FCGDAEB. Start from the first letter, 'F', and count up to G#. (Remember the order is all sharps.) FCG is the end of our counting, because 'G#' is the last sharp in that order.
So, F# C# G#, 3 sharps, are found in the Key of A Major. The A Major Scale has these 3 sharps also. Scales are just note patterns within a single Key, so we know which notes to put in the pattern, using every letter.
Now, when we play a song in the Key of A Major, we know the Root is 'A', and that we will play 3 notes, FCG, all sharp. That's why the scale of A Major looks like this:
Notice that the scale sharps are not in the same letter order, as the Order of Sharps, FCGDAEB. This is because a scale has a sound or tone, and the Order of Sharps is only a step counting tool to find the Key.
Opposite sharps, a song can have only flats. For example, we may be playing a song in the Major Key of Eb. The scale notes in that Key are:
This scale has 3 flats (BEA flats). The Key for Eb uses the Order of Flats for finding the number of flats. Here is the Order of Flats:
This order is a tool, to only count the number of flats, in a Major flat Key. To find the number of flats in the Key of Eb, we use the Root, Eb, as the second to last flat.
Count up to that note in the Order of Flats: BE, then add the last flat to complete the number: BEA flats. So, 3 flats are in the Key of Eb Major, which has these scale notes:
Notice these flats are not in the same order as the Order of Flats, because we are following the scale step pattern, WWHWWWH. This pattern makes the sound, but use the Order of Flats (BEADGCF) as a counting tool to find only the number of flats, not to determine the sound of the scale.
Allow me to add that the Root note is the name of the Key, and the Order of Sharps or Flats are tools to find the number of sharps or flats, for that Key.
The Sharps use a half step below the Root, to find the number of Sharps.
The Flats use the Root as the second to last flat, to find the number of Flats. Here is their Order:
The flats are the sharps' order backwards, or reversed.
A phrase to remember the Sharps' order is:
To remember the Flats' order, use:
2wholes, 1half, 3wholes, 1half steps
These steps distance the tones apart, to sound like a Major Scale pattern. You can start on any note (root), and use this pattern of steps between each note.
The half steps will fall on the 3rd and 7th notes. Remember that B to C and E to F are half steps.
C w D w E h F w G w A w B h C
F w G w A h Bb w C w D w E h F