A good light and a dark room are the basic tools.
At 10 days with chicken eggs, you should be able to see the veins and the embryo. Look for what looks like a spider web with the spider in the middle of it. The dark spot will be the embryo. It could move in response to the light also. The veins are the main thing to look for - the spot could be visable or not at 10 days. It could just be out of sight. The veins are the first really visable thing to develop.
If the eggs are real dark or blue or green, they are harder to see into. If your light is bright enough, you can still see, it is just harder.
To learn the candling routine, I would candle every few days and see how they change with time. As the chick grows, etc.
An egg that is not fertile and not developing will look clear with the orangy blob that is the yolk. Even if you find any of those, leave them in (as long as they don't stink or weep) for a little longer to make sure. You could check a store bought egg to see how a clear egg looks.