Most people feed the chicks Chick Starter, in crumble form. Most people buy the medicated, but many people buy non-medicated.
After that, some people, at 8 weeks of age, switch them to Grower. Others, just keep them on the Chick Starter until the birds are adults. It's a choice.
Once everyone is laying, some people like what is called Layer Feed. Layer is just Grower, but it has added calcium, needed for egg shell production, but others continue with a Grower type feed and offer a calcium source, such as oyster shells on the side.
All major feed companies, Like Purina, off this information, and more, on what is called a Feeding Chart. This Chart is either printed on the back of their bags of feed, and/or available on the feed company's website.