As you set up for the squat, pay attention to bar position and foot width. A high bar position allows your back to stay upright and lets you keep the focus on the quads. With a low bar position, the bar should come across the back around the middle-trap area. This will create far more bend at the hips, and consequently involve more glutes and hamstrings. Some will find they are stronger with a low-bar squat versus the high-bar squat, but I encourage you to play around with both positions and see which one works best for you.
As for the feet width, that's more of an individual preference. Taller squatters will likely have a wider stance, which will target more of the glutes and inner quads, with the opposite applying to the more narrow stance.
If you're trying to maximize your strength on the squat, pick the bar position and the foot placement that allows you to squat the heaviest.
Today's workout starts off with a bang—5 sets of squats at 80 percent of your 1 rep max. There's no prescribed rest in this program; take enough time between sets so that you feel mentally and physically recovered, but don't extended your breaks longer than 2-3 minutes.
There's nothing short about this workout. If you find yourself crunched for time, get through all of the main lifts (squats, leg press, lunges, and RDLs) and skip one of the accessory movements, like seated calf raise, if you need to.