DMX is how a lighting desk talks to the lights. The desk sends a stream of numbers down a cable, and each light listens for its own numbers.
The desk has numbered channels. Each channel holds one number from 0 to 255. Zero means off and 255 means full. A fader halfway up sends about 128.
Every light is given an address, which is the first channel it listens to. A simple light needs one channel for its brightness. A moving head needs eight in a row: intensity, red, green, blue, white, pan, tilt and zoom.
The lights are linked one after another on a single cable. Every light hears every number but only reacts to the ones at its own address. One cable carries up to 512 channels, which is called a universe.
The Grand Master and Blackout only change the intensity channels. Colour, pan, tilt and zoom keep their numbers, so a moving head stays pointing where it was.
Push fader 1 halfway and watch its DMX number become 128. Then switch on Moving heads and try to light one. It needs intensity, a colour and the right position all at once.