The old riddle, "Which came first, the chicken or the egg?", would be appropriate here. To get started you could begin with fertile eggs from a hatchery or a local homesteader, place them in an incubator, turn them 5-6 times a day and in roughly 21 days, you'll have some chicks. (See incubation) The problem I have found with this method is that your success rate is going to be really low. If you ended up with a 40% mortality rate, you would be considered very lucky. This can be very discouraging.
The next option to consider is ordering day-old chicks. This is an excellent way to begin, it's fascinating to watch the chicks and encouraging to see them grow. For this method you will need a brooder, and carefully moniter the temperature in the brooder for a few days before you get your chicks. If you wait to set up the brooder until the day the chicks arrive you are asking for problems. The size of the brooder will depend solely on the number of chicks you're buying. I find it best to do small numbers at a time, considering the size of the birds when they are a few weeks old and ready to leave the brooder, rather than considering how many the brooder will hold at a day old.
Another option, especially if you want eggs now, is to buy grown birds. Many times you can buy spent layers for very little money from commercial poultry houses. Although considered "spent" by the commercial grower, they may still have many months of laying ahead of them for the homestead. The advantages of this option are that 1)You don't have to worry about a brooder, they can go straight into the henhouse; and 2)You don't have to wait long for eggs.
http://www.mcmurrayhatchery.com/
http://www.idealpoultry.com/
http://www.strombergschickens.com/about.htm
