The mixolydian scale is a handy variation of the major scale. It has the same notes, only with the seventh note lowered by a half-step. This makes it sound a little jazzier than the happy major scale.
The mixolydian scale is a mode of the major scale, meaning it uses the same pattern of notes. The difference is where in the pattern you start. If you play a major scale starting on the fifth note, you get a mixolydian scale.
Let's take a look at each of the hand positions used for this scale. If you haven't already, you may wish to read about bass scales and hand positions first.