In Western music the major and minor scales are the most common scales used to create songs. The Circle of Fifths is very useful for seeing the relationship of the major keys to their relative minor keys.   If you look at the circle you will see that each major key is exactly 1 and 1/2 steps above its associated minor key.  For example G is exactly 1 and 1/2 steps higher than it's associated minor key Em.  E-F-F#-G.  This is true all the way around the circle.  

On the violin neck a half-step is one finger placed right next to another finger -- more or less.  A whole step leaves a finger-width between one finger and the next -- more or less.  Placing a finger on any note on the violin and walking backwards three half steps will always be the name of the relative minor key of the note you played. 

A Major Scale "Do Ra Me Fa So La Te Do" is composed of two four note groups separated by a whole step.   Each four note group (called a tetrachord) follows the pattern Whole Step - Whole Step - Half Step.  Below I show the tetrachords along with the scale number of each note from 1 - 8, with WS indicating a Whole Step and HS indicating a Half Step. 

1st tetrachord : 1-WS-2-WS--3-HS-4

Separator: WS

2nd tetrachord 5-WS-6-WS-7-HS-8. 

Following that pattern from anywhere on the violin you will be playing a major scale that is named for the first note that you play. 

Notice on the Circle of fifths, next to the letters for the keys, there are key signatures which may contain sharps # and flats b. Once memorized one can tell instantly what key (the first note of the scale) the song is played in.  For example G has one sharp, the F# which is the 7th note of the G scale and is, as can be seen in the tetrachord above, 1/2 step away from the octave. 

To play the associated minor key (which has the same key signature as the major key) start the scale on the note 1 and 1/2 steps below the first note of the major scale.  For G major that note is E.  So starting on the E and ending on E, play all of the same notes as the G scale and you will be playing in E minor.  That is E-F#-G-A-B-C-D-E.  You will notice that the half-steps are not in the same places in the tetrachords as they were in the major key.  This difference in note intervals is what gives the minor key its distinct sound. 

However, there are actually three minor scales.  I will mention that if you want to experiment with scales that sound more Eastern than Western, the Harmonic Minor scale might be interesting.  To create the Harmonic Minor simply lower the 3rd and 6th notes of any major scale by 1/2 step.  For example, the G Major Scale G-A-B-C-D-E-F#-G.  The G Harmonic Minor: G-A-A#-C-D-D#-F#-G. 

Hope this helps. 

Raven said
Ooohh,oww,ouch! The more I learn, the more I see I am way behind! Going to have to get out the slide rule for this. But that's okay, I like math. Just don't expect to have any esoteric discussions about the subject with me for a while! Thanks for going through the trouble of finding these links for us!  

Music theory is interesting, but keep in mind that all the music theory in the world won't beat a good ear.