Mixolydian scale for guitar
The Mixolydian scale, or mode, is the fifth of the seven musical modes. It is similar to the major scale except for the lowered seventh. The Mixolydian scale is the scale that appears when a major scale is played with the fifth note (fifth scale-degree) as the root. Thus, a C major scale played from "G" is a G Mixolydian scale. This is why the term "mode" is more appropriate than "scale".
The G Mixolydian mode is the same as a C major. So what's the difference? There is no difference; it's the chords that create the magic. Playing a G Mixolydian scale over a C major chord will sound exactly like playing a C major scale (because they are identical). However, playing a G Mixolydian scale over a G major chord will sound "Mixolydian".