Candling is when you shine a bright light through the egg so you can see what's going on inside. Kind of like 'ultrasound' for chicks. We used a bright desk lamp with a movable neck and I made a cardboard table with a small cutout for the light to shine on the egg. This way, we were able to set the egg down on the 'holder' and take pictures!. We only candled three eggs tonight and all of them looked good! It is normal to loose a bunch- especially first timers like us, so the fact that we randomly picked three good ones out of 18 seems like a great sign to us!
Here's one, but I bet my husband's photos were better. I'll try to get them up too.
The spidery veins and dark spot is the developing chicken: