This Weekly Workout is titled Flat Keys & Open Strings which will teach you how to use open strings in melodies, chords, and arpeggios when playing in a variety of flat keys. From Scott Nygaard's introduction:
When guitarists talk about guitar-friendly keys, it's almost always the sharp keys C, G, D, A, E all guitar friendly and all with sharps in their signatures, not flats. Some flat keys are called horn keys and are no fun for guitarists. Or are they? Because one of the things that makes something easy on the guitar is the presence of open strings, let's take a closer look at a few flat keys and see how many standard-tuning open-string notes can be found in them.
The Weekly Workout is a series of monthly exercises made up of interesting technical workouts that will get your fretting- and picking-hand fingers working in different ways, and offer musical studies that will help you visualize and explore the fingerboard. In every lesson, you'll get a different exercise to work on for each week of the month, as well as a few extra variations and extended practice ideas. Although we're presenting these as weekly exercises, there are numerous ways you can approach them, of course. Do whatever feels right for you.