If your check engine light is on, click 01-Engine . The status bar at the bottom will change from "Not Connected" to "Ready." You have now successfully performed a VCDS open controller action.

In automotive diagnostics, a "Controller" is the Electronic Control Unit (ECU) responsible for a specific system. Your car isn't one computer; it is a network of 20 to 80 small computers. The command is the digital handshake that allows VCDS to communicate directly with one specific ECU.