Aperture: The iris. It's measured in F - stops. The higher the F - stop is the higher the iris walls are which lets less light in, this means the lower the F - stop is the lower the walls and more light is able to come in. The iris controls where the light hits the sensor.
Shutter Speed:The speed of how fast the photo is shot. The shutter speed is is measured in fractions like 1/1000. To pick up a very detailed shot you want to have low shutter speed in low aperture. To capture a fast moving object you want you shutter speed to be fast.
ISO: This is measured in numbers 100. High quality, high light = no movement. Low quality, low light = a lot of movement.