Pixels in your cameras sensor pick up light. This light is converted into an electrical impulse which is then transferred as an image to your LCD camera screen or stored on the memory card.
Sometimes the electrical signal is not clean but muddied and noisy. This can lead to a degradation of the image especially visible on a printed or computer screen enlargement.
This happens through natural variation, internal electricity generation (the internal activity of the sensor) and temperature changes.
Noise becomes apparent on the image as an unnatural variation in colour of small spots or areas. This is especially so where the image is a uniform colour such as sea, skies and large flat surfaces which are evenly lit. In the days of film, we would call this grain. But, whereas grain could be used to creative effect, noise is usually unwanted. In general, there is little you can do to avoid it except pay for a more expensive camera.
Noise wont be a big issue for you although you may notice it. A lot of people talk about it as if good photography and perfection are equivalent qualities. It is often more apparent in compact cameras than SLRs and, of course, professional level SLRs have the least noise of all.
There are ways of reducing noise but they involve software manipulations which are reasonably detailed. Unless you are a perfectionist, it might be best to use your energies elsewhere and let the purists worry about a few stray pixels here and there.
Eric Hartwell runs the photography resource site http://www.theshutter.co.uk and the associated discussion forums as well as the regular weblog at http://thephotographysite.blogspot.com.
