There are hundreds of thousands of dog put to death yearly in the United States and a large percentage of them come from people who breed casually without knowledge or experience, called backyard breeders.
If you are not willing to do at least the minimum of a year of research and education on the breed you've chosen and on veterinary science & genetics in general and if you are not prepared to be responsible for every puppy you allow to be born (that includes those that people return to you for one reason or another), then stop now and THINK!
If you are still persistant, please read the following two articles written by experienced breeders: