How does natural selection form wings?

Something that confuses me. Natural selection is when the species best fitted for survival lives while those not die off. This is what happened with the giraffes seeing as how giraffes once had much shorter necks. How did the dinosaurs evolve into birds? I know that Velociraptors had feathers and they might have been the first formations of reptile to avian evolution but why is there a need for flight? The velociraptors were expert hunters comparable to wolves so what was the need for natural selection. Still don't understand evolution fully so don't comment about how ignorant I am, because yes I am ignorant on this topic.