The hen will typically keep sitting for a bit, because she's waiting for the newly-hatched chicks to dry off, and for the rest of the chicks to finish hatching. (They won't, but she doesn't know that. She just keeps sitting for some amount of time after she has wiggly, peeping chicks.)
If you put food and water near the nest, the hen will be able to grab bites of it, and the chicks will probably pop out to have some too. For this, I like to put a little bit of chick starter on small dish (like a jar lid), and add water until it's a soggy mush. That does not spill the way water would, and the hen & chicks get both food and water as they eat it. Mine have always seemed to like it.
Within a day or two, the hen should come off the nest with the chicks, and lead them to food and water. She just needs a bit of time to adjust from "sit on eggs" to "care for chicks."