How many channels the Audio module uses is set on the module: click its screen.
Patch a Link Send module to offer audio to other apps; a Link Receive module plays a channel from another app (click its screen to pick one).
Dark or light module panels; the rack around them stays dark.
Module packages in this folder load when Kabelwerk starts:
A package is a folder with module.json, module.cpp and optionally ui.js. To make one, use New Module in the toolbar (⇧⌘N). Help → Documentation explains the rest.