A cable release enables you to release your camera's shutter without touching your camera (and consequently risking a little camera shake). You can buy wireless releases (below left), and wired versions (below right).
- the electronics need to be compatible with the electronics in your specific camera model - as does the socket fitting.
Some cable releases just release the shutter for you, while others incorporate a timer. This can be important because often your camera will allow a maximum timed shutter speed of 30 seconds, and you may want to exceed this. Some camera models do have a built in timer also, so it is best to check if yours does - if it does, settint it will ive you an alternative to using the cable release. We tend not to use our camera's timer - preferring to set the camera to "bulb" exposure (the camera keeps the shutter open for as long as you press down the shutter release), and count or manually time the exposure. You can lock the cable release button down, so you don't have to keep hold of it.
As models differ according to which camera you have there is no one size fits all, so it would be impossible to give you a specific recommendation. We will say that we have had problems with a non Nikon branded cable which was faulty - but that was probably just bad luck. We now use branded Nikon. If you go off brand however you do tend to pay less.