drcausey

I'm new to this and I don't understand how, when you are learning to pick scales with the right hand, do you know which fingers to use in which frets with the left hand?

Usually in the lesson the instructor will show you the fingering. If you're just looking at a scale pattern that you'd like to play, with absolutely no idea on the fingering, then use efficiency of motion to guide you. Using all four fingers, which requires the least amount of movement to reach to the next note? You're going to have to hop up or down a fret at times, but if you're hopping up two or more frets, there's probably an easier fingering that you could use.