Putting on the girth belt is actually incredibly complicated. As you are facing the rear, the right side is sewed on to the end of the girth belt. It is then run under the second rung in the belt on the left side and putting the prong through a hole in the belt, then running the belt over and under the third rung on the left side and bringing it back across to the right side and going under the first rung, putting the prong through another hole in the belt, and running the belt over the second and third rungs and tucking it under the third rung.
Once you get it right a couple of times, it makes sense, but it is hard to figure out the first couple of times. As to tightness... I make mine tight. The lower belt needs to be tight over the kidney plate. Otherwise, it will fall down under the kidney plate and it will look sloppy. The top part can be as tight as you want, but I prefer that to be tight on me too, primarily just to hold my gut in.