Panhard rod is the bar that runs from the front axle to the frame. It's the bit that keeps the axle from moving sideways. The bushes are pressed into the ends.
Re the joint: What it does is allow you to reset the pinion angle of the rear axle after you've lifted the truck. Essentially rolls the axle to allow the driveshaft to realign better. I've got a 2" lift on mine, and have no worries without it. I'd consider it if you go 3" or more of lift, or are having vibration issues from the rear shaft.