| There are all kinds of different scales, Major, Minor and probably an unknown number of modes and jazz-type scales. They are a lifetime study.
Basically a scale is a form of organization for a set of notes that span an octave. Just what notes they are will determine the way the music sounds. Major vs. Minor is only one example of a different sound.
Major = C D E F G A B C
Minor = C D Eb F G Ab Bb C (there are at 3 different forms of minor scales, each with its own unique sound. Some people would call this example "pure" minor, other would call it "Aeolin"... both are right)
From the collection of notes that make up a scale you can select different notes at different durations and make up melodies. So the 'sound' of the scale will have an affect on the 'sound' of the melody.
Harmony is made up of the notes too, so different scales sounds will affect the harmony made from those notes.
Through the course of a song many different scales can be used so, for instance, you could have melodies and harmonies in the first 4 measures made from a C scale, and then the next 2 measures could use an F scale. Later on you might find that's the G mixolydian (that one of the modes) scale is used etc etc etc.
Scales are the building blocks of western music. You will never know enough about them. Learn to love them, they will be with you as long as you play and create music.
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Never confuse beauty with things that put your mind at ease. -Charles E. Ives
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