What is the fastest way to learn scales on the guitar? Is there anyplace with an explanation for scales?

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I just started learning guitar on a more than casual basis.
I just started learning guitar on a more than casual basis. I can play by ear but I realize that I am cheating myself out of an education. I need an explanation for the why do scales work and how they fit together.
I understand learning scales are fundamental to everything else but what I don't understand is why?

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