Jacob, having nothing, begins the process of building some holdings of his own. First, whenever the animals were mating he had them face either the striped branches or the streaked and spotted animals of the flock. It seems that Jacob believed that if an animal looked at the striped or spotted branch or the stripped and spotted members of the flock, they would deliver a stripped or spotted offspring. Second, Jacob engages in a little selective genetics. He only puts the sticks out when the strong animals are mating.
Commentators disagree at what was really happening here.
Some suggest that Jacob was up to his own schemes and was relying on superstition to get himself a flock. Others attribute great wisdom to Jacob. They see in Jacob an expert in sheep who knows what works and uses his knowledge to get a flock of his own. They believe that Jacob knew some scientific fact that we don't know about. But I don't think that is the case.