ISO Test Image

Part A:

Aperture doesn't not have two Ps. 

Part B:

Shutter speed is how much time the camera's light sensor is exposed to light. Thus, the greater the shutter speed, the greater will the brightness of your image will be and the smaller the shutter speed, the lower the brightness of your image will be. The highest shutter speed a fairly expensive camera can handle is usually about 1/4000s and the lowest is typically about 30 seconds. You most be carful when you raise the shutter speed too much and don't change the other exposure settings ( ISO and Aperture) because it can your image to be too bright and too bright image is not possible to recuperate because all your information is lost. Shutter is speed is the first exposure setting that you usually want to adjust/change when you want to shot a action shot. 

Aperture is how much of your lens is open and exposed to light.  This also depends on the same principle as shutter speed: The greater the Aperture, the greater the brightness of your image and smaller your aperture, the lower the brightness of the image. The aperture also changes the depth field range, a term for the area of an image that is focus. So if you want to take a nice portrait you want to take your shot with a wide aperture so the only thing focus in your picture is your subject . Whereas, if you want a take a picture of  mountain you want a smaller aperture to get in focus on all the mountain.

ISO measures the sensitivity that that  image sensor is to light. Therefore the greater the ISO, the  more sensitive is your image sensor making your image brighter. For that reason a high ISO can help you capture a image in dark areas. However, there is a side effect when you raise the ISO to much: it causes your image to have a lot of grain or noise. Aperture and shutter speed are usually the first setting you want to change in your camera, whereas the ISO is the last t.