The aperture controls the amount of light that passes through the camera lens. When you press the shutter button on your camera, you are opening the shutter to allow light to pass through the lens and create an image of what the lens sees. It’s just like how your eyes work to create pictures in your brain of what you are looking at. If you shoot with the aperture adjusted to the smallest opening, the smallest amount of light is allowed to enter. For example, if you are taking a photo in an environment that’s too bright — how should you adjust your aperture? Simple — adjust to smaller aperture to let in less light. The aperture’s sizes are measured by f-stops. A higher f-stop means a smaller aperture hole while a lower f-stop means a bigger aperture opening. Aperture refers to how wide or narrow the lens opens. Lenses these days open in a rounded motion, so your aperture is a circle (or a polygon, like an octagon, that is close to a circular shape). How wide or narrow it opens determines how much light can get through the lens at one time. Then your shutter speed determines how long the shutter stays open. Again, think about your eyes. Your pupil works like the aperture of your camera. When lighting is dim, you iris (colored part of your eye) will dilate your pupil (the black part) to a large aperture to allow more light to the lens of your eye. When you are in bright light, your pupils get really small, like a narrow aperture, to allow in less light.
Note: Remember that larger apertures are the smaller numbers on the camera settings, like f/1.2. Smaller apertures are the larger numbers, like f/22. This is important understand when you are setting your aperture.