There really isn’t a whole lot of stuff that makes a basic camera work.  I mean, modern cameras have built in computers, light sensors, motors and digital cameras have CCDs and large screens.  All of those things are modern invention and aren’t really necessary to take a picture.  What a camera needs is a lens to focus the light and a way to block out the light before and after the picture is taken.

If you think this sounds too simplex then look into making a pinhole camera.  That would be nothing more than a piece of film in the back of a dark box, a small whole to let in light and then something to cover the hole with.  That’s a fully functional camera.

The shutter, the thing that covers the hole, is one of the two most important aspects in the science of photography.  (The other is aperture which, in a nutshell, is the iris of the camera.) 

Before learning about art and composition a photography student must know how to measure the light entering the camera.  Too much light will overexpose the picture and too little light will underexpose the picture.  The light can only enter the camera when the shutter is open.  The length of time that the shutter is open is referred to as the shutter speed.

Therefore, you should be able to see that by merely adjusting the shutter speed you can control how much the picture is exposed.  In a situation where the subject is lit by the sun, the shutter speed would have to be fairly fast.  If the subject is being lit by a candle then the shutter speed would have to be very slow. 

Recognizing what is fast and slow can take some getting used to since the typical photo is captured in a fraction of a second.  A sunlit photograph may be taken 1/250 of a second or even 1/1000 or 1/2000.  When the photo is taken with a flash the shutter speed is usually 1/60 or 1/90 of a second.  Incidentally, these numbers usually appear on a camera without the “1/” and instead are displayed as 1000, 250, 90, 60, etc.  For shutter speeds longer than a second it would appear 1’’, 2.5’’, etc. 

An automatic camera will set the shutter speed all by itself, but there are times when it is still worthwhile to adjust it manually.  Most obviously, there may be a time when you actually want an underexposed shot or an overexposed shot.  Sometimes the photographer may want to get creative and have a subject blurred by movement; to do this there would be a shutter speed of maybe a second or more (and the aperture closed tight to avoid over exposure) and the subject will simply move across the frame. 

When experimenting with the various shutter speeds on your camera it’s important to keep in mind that the shutter speed and aperture work together.  Usually, when you adjust one you must also compensate by adjusting the other. 

Also, try to get your head around the idea that a lot can happen in a second.  A photo taken at less than 1/60 of a second can easily blur due to camera shake and the subjects movement.