There are three main settings which combine to give you the exposure, these are aperture, shutter speed and ISO sensitivity.
Aperture is best explained as the diaphragm opening inside a lens. This setting in short determines the depth of field, the portion of a scene that appears sharp in the image.
Shutter speed and exposure time are the same thing but different terms used to discuss the length of time the shutter is open. This setting may be used to blur or freeze motion.
ISO sensitivity is just that. What ISO denotes is how sensitive the image sensor is to the amount of light present. The higher the ISO, the more sensitive the image sensor and therefore the possibility to take pictures in low-light situations.
If you are using a point and shoot most cameras take care of these settings for you. However if you are using an advanced point and shoot or a digital slr you should have the option to set the time the shutter is open and the aperture setting or f-stop. Many cameras also give you the option of aperture priority or shutter priority as well as manually selecting both.
Shutter speed is a very interesting option that along with the aperture setting will control how your picture looks as an end result. One is dependent on the other.
If you set the shutter speed for too long, for example 1/4 second in a well lit situation with a large aperture setting such as f-18 it will be over exposed and can even have a black and white effect or possibly totally white. On the other hand if you set the shutter speed for too short of a time for example 1/1000 second and a small aperture setting such as f-4 in a low light situation it will be underexposed and be very dark possibly even completely black. These are exaggerated examples.
In the previous examples if you can change the ISO setting it is possible to obtain different results. If there is not enough light to get the correct exposure you could select a higher ISO setting however this may result in “noise”.
You may want to start by using your camera in automatic mode and see what the settings are and then tweak them to get the results that you want. This can be a lot of fun. I especially like to experiment with these settings when taking pictures of waterfalls and pictures at night of moving lights.
This article is just the tip of the iceberg when it comes to learning about the aperture, shutter speed and ISO settings. I hope you will experiment and have lots of fun!