A Mixolydian scale on the guitar fretboard
The A Mixolydian scale is made of A (the root), B (major second), C# (major third), D (perfect fourth), E (perfect fifth), F# (major sixth) and G (minor seventh). The fretboard shows every one of them across the neck in standard tuning (E A D G B E), and plays them back so you can hear the scale.
The Mixolydian mode is a major scale with a lowered seventh, the fifth mode of the major scale. It shares its notes with a major scale a fifth below, so one set of positions serves both. It is the scale that fits the dominant seventh chord.