Updated: Nov 15, 2018
The shutter is a small “curtain” in the camera that quickly rolls over the image sensor (the digital version of film) and allows light to shine onto the imaging sensor for a fraction of a second. The longer the shutter allows light to shine onto the image sensor, the brighter the picture since more light is gathered. A darker picture is produced when the shutter moves very quickly and only allows light to touch the imaging sensor for a tiny fraction of a second. The duration that the shutter allows light onto the image sensor is called the shutter speed, and is measured in fractions of a second. So a shutter speed of 1/2 of a second will allow more light to touch the image sensor and will produce a brighter picture than a shutter speed of 1/200 of a second. So if you're taking a picture an it is too dark, you could use a slower shutter speed to allow the camera to gather more light.
The aperture is a small set of blades in the lens that controls how much light will enter the camera. The blades create a octagonal shape that can be widened, or closed down to a small hole. if you shoot with the aperture wide open, then more light is allowed into the camera than if the aperture is closed down to only allow a tiny hole of light to enter the camera.
Aperture sizes are measured by f-stops.
A high f-stop like f-22 means that the aperture hole is quite small, and a low f-stop like f/3.5 means that the aperture is wide open.
is an acronym, but nobody really knows what it stands for. It is always just called ISO even though it really stands for International Organization for Standardization ISO controls the exposure by using software in the camera to make it extra sensitive to light. A high ISO such as ISO 1,600 will produce a brighter picture than a lower ISO such as ISO 100. The drawback to increasing the ISO is that it makes the picture noisier.