When we take a photograph the shutter snaps open and closed. The aperture is how wide that doorway to our camera opens. Imagine the shutter as a doorway, the stops go behind the door and so a large stop say F/16 only allows the door to open a little. At f/30 and we have a tiny pinhole and at f/3.5, on most lenses, it wide open. On my 35 mm prime lens, wide open is even wider at f/1.8.