Aperture controls the size of the lens opening which allows light into your camera.
Opening the lens more or having a low f-stop number (e.g. f/1.4) blurs the background/foreground around your subject. This is known as a shallow depth of field.
Keeping the lens more closed or having a high f-stop number (e.g. f/16) keeps the photo sharp throughout. This is known as a wide depth of field.
Shutter Speed
Shutter Speed is the amount of time the shutter is open to expose the image sensor to light.
Slow shutter speeds expose more light to the image sensor so still objects will have more detail and moving objects will appear to have more motion/be blurry.
Faster shutter speeds means less light is exposed to the image sensor and moving objects appear more still.
ISO
The ISO of a camera selects how much light the image sensor detects.
Too much light on a sunny day can cause overexposed shots so a lower ISO would be preferred.
Too little light in a shady room or day can cause grainy images.
The general rule is to use the lowest ISO possible to get the most detail possible.
Exposure Meter
The Exposure Meter is your final check before you snap a shot. It shows you how well your aperture, ISO and shutter speed are working together.
It is used as a guide to show exposure.
White Balance
White balance is the ratio of blue light to red light in an image which refers to the concept of colour temperature.
White balance is measured is Kelvin(K). Higher values of Kelvin contain more blue light whereas lower values of Kelvin contain more red light.
Here is a table of Kelvin which shows the colour temperature of possible subjects. You can see that a cameras electronic flash is similar to sunlight.
Below is an example of an image in a warm lighting that has the correct white balance next to a copy with too high a Kelvin value. The image is more yellowish because it is expecting excessive blue light but the image is only being lit with reddish lights.
Here in this image the camera is set to a low Kelvin value (which tells the camera to absorb more red light) in sunlight. This results in a bluish image.
