Within your script, you define a trigger channel and button to use to start your show. When you are ready to begin the show, go to the channel that you specified and push the trigger button that you assigned. For example, you may define your trigger channel as 00 and your trigger button as 1. After arming the controller, go to channel 00 and press button 1, and the script will start. You can also use "AUTO-FIRE" or "STEP" as the trigger button.
For more information on defining trigger channels and buttons within a script, please see our 18R2 Controller User Guide and 18R2 Example Script Template.