Here is a link to the site I used a lot to learn more. It is for duck eggs, but the basics are the same. Look around the whole site, they have a lot of good info on it.
http://www.minkhollow.ca/HatchingProgram/Candling/index.html
The big difference between chicks and ducks is the time...
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...