I am part way through this. My chicks are a month and a half old. A friend gave me 5 fertilized eggs when my buff orpington went broody. The quick answer is she'll do almost all the work. Exactly 3 weeks after the eggs were set, the chicks (only 3 of the 5) hatched and came out for a look around. Don't let your other chickens get at the chicks. One of mine was adventurous, and was killed. But, now they are in a separate pen. The broody will peck food out and drop it for them. She will do it with berries and with meal worms, too. She will be very protective, so wear gloves. It's all a learning experience. Both the broody and the chicks will eat chick feed. It's available as either medicated or non-medicated. I used non-medicated and have had no problems with pasty butt or coccidiosis.
One thing to watch for is that the broody will get up once a day from setting to eat and to poop. I found that while she's up, the other hens will get in her nest box and lay eggs. At the time of hatch, she had 14 eggs under her (only five were in the original clutch).
