Getting started with the DMX dimmer

Things you will need

DMX is a protocol to control all kinds of stage equipment, from smoke machines to robot lights.
DMX is a standard used world-wide, if you master DMX you can go to any theatre or club in the world, plug your laptop and control most of the equipment there.
A DMX signal is composed of channels and universes. Each Universe has 512 channels, and each channel can carry one number between 0 and 255. Channels can be used to carry information. For example, imagine we have a DMX light with RGB LEDs, many of these lights use 4 channels. One channel for RED, one for GREEN and one for BLUE and a fourth channel for INTENSITY. So a DMX data stream to make that light bright pink would look something like 255 0 255 255.
All DMX devices let you configure which channel they start on, so if you set your light to start on DMX channel 5, and it uses 4 DMX channels for itself, then the channel numbers for the light would be 5, 6, 7 and 8 for R, G, B and INTENSITY respectively.
One of the original purposes of the internet was to host manuals for DMX devices in PDF. ;) So if you have a DMX device in your hand, it's very likely that you can find the manual (with the channel usage details) if you google for it.