I don't know how much you'll be able to see with your mag light. I fashioned a sort of candler out of a lamp and a flower pot. I've only candled once, but it was really helpful to me to candle an egg from my fridge first. That way i knew what a dud looked like.
It took me a little while, but i was able to start looking for the air pocket on the fat side of the egg and notice the embryo forming - along with veining. Once your eye is trained to it a little, you'll probably be able to see the embryo and the umbilical cord - or whatever it's called for chickens. It's great fun. And my chicks are hatching right now, so i think i got it right. I identified one dud - which definitely turned out to be a dud - and one "that doesn't look quite right," which now doesn't seem to be hatching.
I think it's an experience thing, but you have to start somewhere.