Aperture is the physical opening of a lens. The larger your aperture is, the more light comes into you camera.
Aperture also controls depth of field. Depth of field is how much of your image is in acceptable focus. A larger aperture will give you a small/narrow depth of field (more foreground and background blur). A smaller aperture will give you a bigger/wider depth of field (more things in focus).
Aperture is measured through f-stops. A small f-stop number indicates a larger physical aperture. A larger f-stop number indicates a smaller physical aperture. It might seem a little backwards, but it’s because it’s all based on a mathematical formula. I’ve made a simple diagram to help you understand it a little better.
Your shutter speed is how long or short your exposure takes place for. The longer your exposure is, the more light is able to enter your camera.
Shutter speed will also affect image blur, either through subject movement or through camera shake. When shooting with a fast shutter speed, your camera does not have enough time to register movement of your subject or movement of your camera. You’ll want to use a fast shutter speed when you’re trying to freeze any kind of action. Slower shutter speeds will show any movement of your subject, as well as camera shake. When you’re using slower shutter speeds, a tripod is recommended.
ISO is the sensitivity of your camera’s sensor to light. Higher ISO values make your camera more sensitive to light.
You might now be asking yourself, “If higher ISOs give you higher light sensitivity, then why not shoot with high ISOs all the time?” The negative effect of increasing your ISO is that you will also increase the amount of digital noise, or grain, in an image. To get clean images, you’ll want to use low ISO values and only increase the ISO when you absolutely have to.