An aviator is a pilot. Every aircraft you see in the sky has an aviator in it.
Aviation is the science that makes airplanes and other vehicles that fly through the air. An aviator is someone who flies one of those vehicles. This is kind of an old-fashioned word: these days, you're much more likely to hear aviators referred to as pilots. Some aviators work for airlines, while others own private planes. Helicopters and blimps have aviators too.