What is a Controller?

A “controller” is a device that sends power and data to the lights to tell them when to turn on and off at a particular color and intensity. In the case of DIY pixels, at the simplest it’s usually a waterproof box containing one or more power supplies, a controller board and “pigtail” connectors to connect to the lights. Most WS2811 controllers are very customizable — similar to building a PC — you can choose a motherboard, power supplies, case, connector types, etc. and assemble it yourself, or you can buy one that’s pre-configured and ready to plug in. In the case of Twinkly lights, each string includes the controller and 24 volt power supply, so there’s nothing to think about.

Simple Explanation:
The controller is the middleman between your show and your lights.