I'm really amazed at the variety of answers for this. This is not hard, folks. It is really not. I took the bit in italics at the bottom from My Pet Chicken's site to back up what I am saying, but there are plenty of other sources available for this type of information.
This is for chickens that will become a laying flock. If you are raising them for meat, the answer is different. And different manufacturers do formulate their product differently. Read the bag. It is probably listed on the bag.
The general progression is to start them on Starter, then once they have a good start, grow them on Grower. Then, when they start to lay, switch to Layer. They are all pretty much the same but the big differences are that the Starter has a lot more protein than the other two to give them a good start, usually around 22% protein while the other two should be around 16% protein. I usually feed starter for the first 6 weeks, but some manufacturers recommend to use their Starter for other periods of time.
After they have grown big enough to graduate from Starter, swith to Grower, which should be around 16% protein. This reduced amount of protein keeps them growing at a nice pace, but also allows them to mature at a rate to match their growth.
Then, when they are ready to lay, you switch to Layer. Layer is also around 16% protein, but it contains somewhere over 4% calcium instead of the 1% or so calcium in Starter and Grower. The extra calcium is for their egg shells. You do not want the young growing chicks to eat that level of calcium because too much calcium can cause bone defects or kidney problems in growing chicks. That is not a problem in older chickens but it can be a problem in younger growing chicks. The usual recommendation is to switch from Grower to Layer when they first start to lay or at 20 weeks, whichever happens first.
To complicate it a bit, some manufacturers do not make separate Starter and Grower, but produce a combined Starter/Grower that is about 20% protein. You can feed this from the day they go into the brooder until you switch to Layer.
To complicate it a bit more, some manufacturers make something they call Developer or Grower/Developer. This product only has 15% protein and can be used from 13 weeks until you switch to Layer. Some manufacturers do not make a 15% Developer product. If they don't, no big deal. If they do, you do not absolutely have to switch to Developer. You can continue feeding 16% Grower or the 20% Starter/Grower until you switch to Layer.
You can see from all this that it is not an exact science. The only real rule that should be followed is to not give the growing chicks too much calcium because of the possible bone or kidney damage. I put it like using a sawed off shotgun. You don't have to hit the targert dead center to avert a catastrophe, but you do need to aim in the general direction. Just follow this as best you can, based on what brand of feed you use.
Hope this helps a bit.
Fortunately this one doesn't require much thought! Suppliers have formulated special feed complete with everything baby chicks need. It's called "starter feed" and comes in either "crumbles" or "mash" (referring to how ground down it is). Either is fine. The only thing to know is that if you've had your chicks vaccinated against Coccidiosis, they'll need an un-medicated feed. If not, or if you've only had them vaccinated for Marek's Disease, medicated feed is a great way to keep them healthy those first few months. We also offer a terrific organic chick starter feed.
A question we commonly get is how long to feed baby chicks "starter feed" for before switching to a feed called "grower" or "chick grower". The answer is: it all depends! Each manufacturer formulates their feed differently, so read the label and follow their instructions. Some only recommend the starter for 4 weeks before moving onto grower; some combine both together in a "starter/grower" feed that can last up to 16 weeks, etc.
Customers also will ask us whether they can feed their chicks scraps, or worms and other bugs from the garden... Small amounts of vegetable/dairy should be fine for the chicks (and they'll love it!), and the same goes with bugs and worms. But consider those like dessert, not the main course. Starter feeds contain everything chicks need to survive and thrive, and filling them up with too much of the "other stuff" can throw off their nutritional balance.
Finally, people want to know how much food they should give their birds. The answer is: as much as they want! Don't ration it. Give your birds 24/7 access to all the food they can eat. They're not like dogs. They'll self-regulate.