breeding for roos and hens

[joe17]

I have read a book online called "the mating and breeding of poultry" and they said that you should atleast have two pens where you breed on pen for good cockerels and one pen for good pullets. This confuses me! How do I do that with silkies? I think this is called stud mating or something like that. Anybody else do this? I just thought breed birds that dont have any flaws and are NEARLY perfect.