after doing glute-ham raises I can definately feel it in my lower back glutes and hams, so I believe that I am doing them correctly.
Start off by getting yourself into a pushup postion but keep your knees on the ground as if you were going to do a easy pushup from your knees. Lock your feet/heels under a low bar, under your bed, or you can have someone hold your ankles. You basically are going to pull your body up from the ground, using your knees as an anchor point. Use your glutes/hams to pull yourself up from laying flat on ur chest to being in an upright position, perpendicular to the ground, and then lower yourself back down to the starting position. It is as much an eccentric movement as it is a concentric movement. Therefore try to focus on lowering our body very slowly and if you are like me and aren't strong enough to pull yourself up from the ground using just you leg muscles, then give yourself a small push off the ground with your hands to help you start the motion.
As for good mornings, I've only done them once before and I don't think that I was ready strength or expirience wise to do the efficiently. From what I understand they are a more advanced exercise, but basically stand strait up with the bar on ur back as if you were going to squat. I believe you stand with legs about shoulderwidth apart and you either keep your legs strait or with a slight bend, try them both out and see what feels better. The movement is to bend forward at the waist until your upper body is paralell with the ground and then pull yourself back to the upright starting position, a similar movement to the glute-ham raises, which is probably why they both effect the same muscle groups.
I always tend to feel it in my glutes the second day after I squat, people look at me funny when I say that my ass hurts when sit down, anyways good luck with the glute training.