First, you need a rooster along with your hens. If you don't have a rooster, none of the eggs will be fertile. If you do have a rooster, or depending on the number of hens, one rooster for every 10 to 12 hens, most of your eggs should be fertile. However, there is no way to tell if an egg is fertile. When you go to incubating the eggs, most of them should hatch.
One way to incubate and hatch your eggs is to use a hen. You can't force a hen to incubate eggs, but depending on the variety of chickens you have, some of your hens may go broody, usually in the spring through summer. When they go broody, they will stay on their nest all day. If they stay on the nest for more than 48 hours, what you can do is check and see how many eggs they are sitting on. If they are just sitting on a few, you can remove those eggs, and put up to 12 fresh eggs under her. The reason for this is that you want her to start incubating all her eggs at the same time. She'll do a good job keeping the eggs warm, and when they hatch, she will do a much better job raising them than you can. And you can forget about needing to keep the chicks under a heat lamp and feeding them starter feed.
I've been using my hens to hatch and raise chicks for four years now, and I much prefer it to using hatchery chicks. The chicks do so much better with a mother.
e4dited by staff