Pixels in your camera's 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 won't be a big issue for you although you may notice it. A
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.