What kind of breeding do you want to do? Do you want to merely replicate and sell chickens, or do you wish to improve the breed and put effort into breeding the right way? I'll write out some stuff assuming the latter. For the former, hardly any instruction is required at all.
First off—which breed have you decided on? A beginner to breeding should choose ONE breed and ONE variety. If you stick your fingers into too many pies you'll end up with... a lot of yucky pies. Join the breed club for the one you have chosen. Attend shows, find literature by those that have been working with the breed for decades, read it, and
listen to it. Buy a copy of the APA SOP and study it in every spare moment. Memorize your breed standard. Start out with the best stock you can possibly buy, preferably a started trio from a top breeder. Hatch all you can and learn to cull. Poor quality birds still taste great. Find a mentor if at all possible; going it on your own is near impossible.
I myself am still new to the breeding front and don't know anything, despite Brahmachicken's kind endorsement.
I have only been seriously interested in breeding for a year. I am only repeating here what I have read and been told, but I believe it is sound. Here are a few links that have good information in them.
http://www.the-coop.org/forums/ubbthreads.php?ubb=cfrm
http://showbirdbid.proboards.com/threads/recent
https://www.poultryshowcentral.com/
The exhibition poultry crowd can be a bit, ah, vicious at times. If someone is rude to you when you ask for advice, thank them, file away what they have said, and keep going. There are some truly nice people out there that love to help, don't let a mean person suck the enjoyment away for you. Good luck! Breeding to the standard is incredibly exciting, difficult, rewarding, and fun. You'll eventually find that seeing a bird that just 'looks right' gives you a thrill similar to embarking on a roller coaster. Back lines suddenly become exciting and a well balanced bird is candy to the eye.
As for 'selling chicks', I doubt you are going to want to do that for quite a while. If you sell someone poor quality chicks, that's a ding on your name and your repute. If you sell someone really good chicks.... then they would have been good kept for your breeding pens.
