ISO Test Image

Shutter Speed:
           Shutter speed is the length the sensor is open to the light, the longer the shutter speed, the more light the sensor receives. The faster the shutter speed equals less light entering the sensor equals a darker image. Opposite for a slower shutter speed. Shutter speed is also used for adding or removing blur, so a slow shutter speed will catch your shakiness causing a blurry image. A slow shutter speed will also make a fast image really blurry while a non-moving object crisp. Fast shutter speeds are used more to capture fast moving object or of you are moving quickly and you don't want a blurry image.
Aperture:
           Aperture is used to make objects in the background and or foreground more or less blurred. If you are taking portrait photos and you want to emphasize on the person and not the background, then you use a tiny aperture to make the background very blurry. If you are taking photos of a hallway that is very long and you want the whole hallway to not be blurred, then you set a high aperture. More aperture means less light will enter the camera so the picture will be darker. While a lower aperture means more light will enter sensor thus brighter photo. This is because the aperture is a hole(that allows light to hit the sensor) that gets bigger or smaller depending on the value.
ISO:
           ISO is the sensor's sensitivity to light, the higher ISO the higher the sensitivity to light. The main downfall of iso is the higher the sensitivity the less accurate the pixels are creating noise in the photo. So if you are taking photos of a smooth lighting scene, like the sky, ocean, paper, etc you'll see the noise and it'll look bad. If you are taking photos of rocks, then the noise might not be very noticeable. ISO can be used in harsh lighting conditions to brighten images without having a slow shutter speed. Also can be used to darken bright images.