Photography is all about light. Our photographs are recorded light. How we control the available light and add additional light when needed is basis for all photography. There are numerous controls and methods for controlling light available to today's photographer.
Your camera's light meter is your link to understanding how your camera sees light. This device takes into account all of the settings on your camera (aperture, shutter speed, film speed, etc) and tells you what type of exposure that combination plus the available light will create on film/sensor. The first step to understanding photography lighting is to understand this tool for measuring light.
Now that you know how to read your light meter, you need to understand how the different settings on your camera affect the light itself. Aperture is an adjustable opening inside your camera lens that adjusts the amount of light that can travel through the lens. Aperture is used in conjunction with other settings to control the maximum amount of light that can reach the film/sensor.
Shutter speed is another control used to modify the amount of light that reaches the film/sensor. Shutter speed controls the amount of time the film/sensor is exposed to light. In addition to controlling light, the shutter speed also has the greatest effect on how motion is represented in the image.
Now that you understand the basic light controls within a camera, you need to understand what exposure actually is. Proper exposure does not mean some magical light value or perfectly centered light meter needle. Proper exposure is whatever the photographer intended for the scene in question. If the photographer wanted to underexpose the scene so that much of the detail was lost in shadow, then that is proper exposure for that instance. The trick is to make sure that your exposures are always what you intended when you pressed the shutter button.
When there is not enough light available to record the desired image, photographers often use a flash to add light to a subject. Fill flash is used when there is actually enough light in a scene but it is in the wrong place in relation to the subject.
Sometimes a flash is not the best way to add light to a subject. Reflectors are often used to create dramatic lighting effects outdoors or in situations when flash can not be used. Reflectors can be professionally made or can be simple items such as aluminum foil-covered cardboard. As long as the object will reliably reflect light back towards a subject, it is a reflector.