The process of selective breeding is described in the following video. Note that selective breeding was practiced intuitively long before there was any knowledge of genetics.
Virtually all breeds/varieties of domestic animals and plants are products of selective breeding. Type into your browser: breeds of ______ images/ (insert the specific animal or plant in the blank)
Again, selective breeding was, and may still, be done without knowledge of genetics. It was/is done by intuitively selecting those individuals with the greatest expression of the desired trait and using those individuals to parent the next generation, then continuing this process over many generations, indeed over thousands of years by long lineages of animal/plant breeders.