How does small aperture help you control light?

The aperture is a set of blades that control the opening of the camera lens. It can be a wide opening or a narrow opening. This opening controls how much light will enter the camera. If the opening is wide, obviously large amount of light will enter the camera, but if the opening is small, less amount of light will enter the camera. The aperture is measured in f/stops. A wide aperture is f/1.8 and a narrow aperture is f/20. So if you decrease or increase the size of the lens opening that lets light into the camera, you eventually control the amount of light that gets in.

In a situation where the picture you clicked turned out too bright, how will you fix it?  An over bright picture is the result of more light entering the camera. So you need a small aperture (lens opening) setting to control it. There is an inverse relationship between the f-stop (number) and the aperture. Like a small aperture in f stops is f/22 (larger number) whereas a large aperture in f stops is f/3.5 (smaller number)

Small aperture = small lens opening = large or higher F stop (e.g. f/22)
Large aperture = wide lens opening = small or lower F stop (e.g. f/3.5)

So, simply by choosing a smaller aperture you can cut down the amount of light that gets into your camera.